{"product_id":"lockjaw-trismus-a-complete-guide-to-causes-diagnosis-and-treatment","title":"Lockjaw (Trismus): A Complete Guide to Causes, Diagnosis, and Treatment","description":"\u003cp\u003e\u003cstrong\u003eSummary:\u003c\/strong\u003e Trismus — commonly called \"lockjaw\" — is a condition in which a person cannot fully open their mouth because the chewing muscles stay tightly contracted. This 2026 narrative review from a team at Sapienza University of Rome and IRCCS Neuromed synthesises current evidence on why trismus happens, how it is diagnosed, and how it is treated, and proposes a new way of classifying its causes. The authors split causes into neurological (nervous system) and non-neurological, then further divide each group into structural and non-structural causes. Building on that classification, they propose a step-by-step diagnostic and treatment algorithm that puts \"red flag\" (urgent, potentially life-threatening) conditions first, and that works in both outpatient clinics and hospital settings.\u003c\/p\u003e\n\n\u003ch1\u003eLockjaw (Trismus): A Complete Guide to Causes, Diagnosis, and Treatment\u003c\/h1\u003e\n\n\u003ch2\u003eTable of Contents\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\u003ca href=\"#ddn-key-points\"\u003eKey Points\u003c\/a\u003e\u003c\/li\u003e\n\n  \u003cli\u003e\u003ca href=\"#background\"\u003eBackground: Why This Review Matters\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#how-chewing-works\"\u003eHow Normal Chewing Works\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#neural-control\"\u003eThe Brain's Control of Chewing\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#methods\"\u003eHow the Researchers Reviewed the Evidence\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#classification\"\u003eA New Way to Classify Trismus\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#neuro-structural\"\u003eNeurological Causes with Structural Damage\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#neuro-nonstructural\"\u003eNeurological Causes Without Structural Damage\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#nonneuro-structural\"\u003eNon-Neurological, Structural Causes\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#nonneuro-nonstructural\"\u003eNon-Neurological, Non-Structural Causes\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#table\"\u003eFull Differential Diagnosis List\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#diagnosis\"\u003eDiagnosis: How Doctors Tell These Causes Apart\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#treatment\"\u003eTreatment Approaches Covered by the Review\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#implications\"\u003eWhat This Means for Patients\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#limitations\"\u003eLimitations of This Review\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#recommendations\"\u003ePractical Recommendations\u003c\/a\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003ca href=\"#ddn-faq\"\u003eFrequently Asked Questions\u003c\/a\u003e\u003c\/li\u003e\n\u003cli\u003e\u003ca href=\"#source\"\u003eSource Information\u003c\/a\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003c!-- ddn:keypoints:start --\u003e\n\u003ch2 id=\"ddn-key-points\"\u003eKey Points\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eTrismus, or lockjaw, is a symptom of an underlying problem, not a diagnosis, and it is often under-recognised, especially in sedated or critically ill patients.\u003c\/li\u003e\n\u003cli\u003eCauses are classified as neurological or non-neurological, and each as structural or non-structural, guiding diagnosis and treatment.\u003c\/li\u003e\n\u003cli\u003eDiagnosis relies on clinical assessment plus MRI, CT, EEG, EMG, and trigeminal reflex testing to identify the cause.\u003c\/li\u003e\n\u003cli\u003eTreatment options reviewed include medication, botulinum toxin type A, physical therapy, surgery, and rehabilitation, matched to the mechanism.\u003c\/li\u003e\n\u003cli\u003eRed flags such as rapidly worsening jaw closure, fever, facial swelling, recent dental surgery, or new medication need urgent evaluation.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- ddn:keypoints:end --\u003e\n\n\n\u003ch2 id=\"background\"\u003eBackground: Why This Review Matters\u003c\/h2\u003e\n\n\u003cp\u003eTrismus, commonly known as \"lockjaw,\" is a clinical condition in which a person cannot open their mouth normally. The restriction is persistent and involuntary, and it comes from tonic contraction (sustained tightening) or spasm of the masticatory muscles — the muscles used for chewing.\u003c\/p\u003e\n\n\u003cp\u003eHow common trismus is remains uncertain. The authors state clearly that prevalence (how many people have it) varies depending on which patient group is studied and what is causing the problem. Trismus is also frequently under-estimated, because there are no standardised screening protocols (no routine, agreed-upon checks) and because it is hard to distinguish from other reasons a person might not open their mouth widely. This is a particular problem in sedated patients or those who are critically ill and cannot report symptoms.\u003c\/p\u003e\n\n\u003cp\u003eBecause of these gaps, the authors argue that clinicians need three things: a clearer understanding of the mechanisms behind trismus, a structured way to classify its causes, and an evidence-based algorithm (a step-by-step decision guide) for managing it. Their stated goal is to help doctors recognise trismus early, choose targeted treatments, and ultimately improve patient outcomes.\u003c\/p\u003e\n\n\u003ch2 id=\"how-chewing-works\"\u003eHow Normal Chewing Works\u003c\/h2\u003e\n\n\u003cp\u003eMastication (chewing) is the process that mechanically breaks food into small particles so they can be swallowed and digested by enzymes. It depends on a set of structures the authors call the stomatognathic system, which includes bones, joints, teeth, muscles, glands, and sensory receptors working together.\u003c\/p\u003e\n\n\u003cp\u003eThe mandible (lower jaw) is the only movable bone of the facial skeleton. It joins the skull on both sides at the temporomandibular joints (TMJs) — the jaw joints — which have a condyle–disc structure allowing both rotational and translational movement. That design lets the jaw open, close, move sideways, and jut forward. A fibrocartilaginous articular disc (a cushion of tough cartilage) keeps the bony surfaces aligned and spreads mechanical stress evenly. By contrast, the maxilla (upper jaw) is fixed and supports the upper dental arch.\u003c\/p\u003e\n\n\u003cp\u003eTeeth are arranged symmetrically and are specialised by shape:\u003c\/p\u003e\n\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eIncisors\u003c\/strong\u003e — sharp edges for cutting.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCanines\u003c\/strong\u003e — robust cusps for piercing food and guiding jaw movement.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePremolars and molars\u003c\/strong\u003e — broad, cuspidated surfaces for grinding and crushing the food bolus (the ball of chewed food).\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eThe four main masticatory muscles are the masseter, temporalis, and the medial and lateral pterygoid muscles. The masseter and temporalis mainly raise the jaw, while the pterygoid muscles enable the more complex sideways and forward movements. Accessory muscles, such as the buccinator and the suprahyoid group, help position the food and stabilise the jaw.\u003c\/p\u003e\n\n\u003cp\u003eSaliva and the tongue are also essential. Saliva lubricates the mouth, softens food, and starts enzymatic digestion through amylase and lipase, while also helping food particles stick together into a bolus suitable for swallowing. The tongue continuously repositions food between the chewing surfaces and shapes the bolus. Its intrinsic and extrinsic muscles make it indispensable not just for chewing, but also for swallowing and speech.\u003c\/p\u003e\n\n\u003ch2 id=\"neural-control\"\u003eThe Brain's Control of Chewing\u003c\/h2\u003e\n\n\u003cp\u003eChewing is largely automatic, but it is not simple. It is a highly coordinated, rhythmic motor behaviour that depends on three interacting systems: a central pattern generator, modulation from the cortex (the brain's outer layer), and sensory feedback from the mouth.\u003c\/p\u003e\n\n\u003cp\u003eThe basic rhythm of chewing appears to be generated in the brainstem by a central pattern generator — a network of neurons that produces rhythmic output without needing conscious effort. The key rhythm-generating elements sit in the dorsal division of the main sensory nucleus of the trigeminal nerve (the fifth cranial nerve, which carries sensation and motor signals for the face and jaw). Neurons in this region have intrinsic oscillatory properties, meaning they fire in rhythmic cycles on their own. Electrophysiological recordings and calcium imaging studies have confirmed that they drive rhythmic activation of the trigeminal motor nucleus.\u003c\/p\u003e\n\n\u003cp\u003eThe trigeminal motor nucleus, located in the pons (part of the brainstem), contains separate groups of jaw-opening and jaw-closing motoneurons (nerve cells that directly command muscles). These are clustered separately, with the jaw-closing group being significantly larger and made up mostly of motoneurons for the masseter and temporalis muscles.\u003c\/p\u003e\n\n\u003cp\u003eCortical structures matter too. The cortical masticatory area — located in humans within or next to the primary motor cortex — is the only cortical region whose inactivation significantly impairs chewing. Other regions contribute to controlling orofacial movement, including the primary somatosensory cortex, premotor cortex, supplementary motor area, insular cortex, anterior cingulate cortex, and amygdala.\u003c\/p\u003e\n\n\u003cp\u003eSensory feedback is indispensable for fine-tuning. Periodontal mechanoreceptors (pressure sensors in the ligament that anchors each tooth to the jawbone) provide detailed information about food contact and forces inside the mouth. They come in two subtypes: fast-adapting receptors, found mainly in the molars and active during the early phase of jaw closure, and slow-adapting receptors, found in the incisors and active throughout the entire closing phase. When these receptors are inactivated, the chewing sequence breaks down, including the ability to regulate bite force and fine oromotor control.\u003c\/p\u003e\n\n\u003cp\u003eMuscle spindles — stretch sensors particularly rich in the deep layers of the masseter — also contribute to orofacial proprioception (the sense of where the jaw is and how hard it is working). Notably, spindles are absent in jaw-opening muscles but plentiful in jaw-closing muscles.\u003c\/p\u003e\n\n\u003cp\u003eThe authors stress that understanding this neuroanatomy is not academic. It is the prerequisite for interpreting what goes wrong in trismus and for designing targeted diagnostic and treatment strategies.\u003c\/p\u003e\n\n\u003ch2 id=\"methods\"\u003eHow the Researchers Reviewed the Evidence\u003c\/h2\u003e\n\n\u003cp\u003eThis is a narrative review, not a systematic review. The authors followed SANRA (the Scale for the Assessment of Narrative Review Articles) recommendations as a quality guide.\u003c\/p\u003e\n\n\u003cp\u003eThey searched six databases: MEDLINE, Scopus, PubMed, Web of Science, EMBASE, and the Cochrane Library. Their search terms included \"trismus,\" \"jaw dysfunction,\" and \"treatment of trismus,\" with specific terms such as \"botulinum toxin type A\" and \"BoNT-A\" added for trismus treatment. Boolean operators (AND, OR) were used to refine results. Terms related to tetanus, such as \"tetanus trismus\" and \"tetanus lockjaw,\" were also included.\u003c\/p\u003e\n\n\u003cp\u003eStudies were included if they:\u003c\/p\u003e\n\n\u003col\u003e\n  \u003cli\u003eWere published in peer-reviewed journals.\u003c\/li\u003e\n  \u003cli\u003eProvided clinically relevant data, case reports, case series, or expert reviews on the etiology (cause), pathophysiology (disease mechanism), diagnosis, or management of trismus.\u003c\/li\u003e\n  \u003cli\u003eReported interventions such as pharmacological therapy, botulinum toxin type A, physical therapy, surgery, or rehabilitation.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003cp\u003eBoth neurological and non-neurological causes were considered, including structural and non-structural factors.\u003c\/p\u003e\n\n\u003cp\u003eStudies were excluded if they:\u003c\/p\u003e\n\n\u003cul\u003e\n  \u003cli\u003eWere not published in English.\u003c\/li\u003e\n  \u003cli\u003eFocused solely on animal models or in vitro (laboratory dish) experiments without translational relevance to patients.\u003c\/li\u003e\n  \u003cli\u003eLacked direct clinical applicability, including editorials, letters, conference abstracts, non-peer-reviewed publications, and anecdotal reports without sufficient clinical or scientific detail.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eBecause this is a narrative review, the authors note these criteria were used as a guide rather than a rigid filter. They deliberately allowed flexibility to include seminal, highly cited, or otherwise clinically significant references, even when those papers did not meet every inclusion criterion. They also manually searched the reference lists of retrieved articles for additional studies.\u003c\/p\u003e\n\n\u003ch2 id=\"classification\"\u003eA New Way to Classify Trismus\u003c\/h2\u003e\n\n\u003cp\u003eThe authors propose a refined etiological classification of trismus. The first split is between neurological and non-neurological causes. Each of those categories is then divided into structural and non-structural causes. Neurological causes are further divided according to whether they involve the central nervous system (CNS — the brain and spinal cord) or the peripheral nervous system (PNS — the nerves outside the brain and spinal cord).\u003c\/p\u003e\n\n\u003cp\u003eThe organising principle is that all forms of trismus, whatever the trigger, ultimately result from dysfunction of the masticatory system. This is the framework the authors use throughout the review, and the one their diagnostic algorithm is built on.\u003c\/p\u003e\n\n\u003ch2 id=\"neuro-structural\"\u003eNeurological Causes with Structural Damage\u003c\/h2\u003e\n\n\u003cp\u003eStructural lesions — physical damage — to the central nervous system can cause trismus, particularly when they disrupt the motor pathways involved in chewing.\u003c\/p\u003e\n\n\u003cp\u003eIn diffuse axonal injury (DAI), a subtype of traumatic brain injury (TBI), widespread shearing of white matter tracts (the brain's long-distance nerve fibres) compromises both voluntary and reflex-based control of orofacial movements. This often shows up as increased tone in the masticatory muscles, contributing to trismus. Post-stroke trismus is most frequently associated with lesions affecting the corticobulbar tract (the nerve pathway running from the cortex to motor nuclei in the brainstem). Damage along this pathway leads to disinhibition of brainstem motor nuclei — a loss of the normal braking signals — resulting in hyperactivity and sustained contraction of the jaw-closing muscles.\u003c\/p\u003e\n\n\u003cp\u003eBrainstem lesions from any cause — demyelinating, neoplastic (tumour-related), inflammatory, or traumatic — can interfere with the descending inhibitory control that normally regulates masticatory motor output. When that inhibitory modulation is lost, muscle tone rises abnormally, producing persistent and often severe jaw closure.\u003c\/p\u003e\n\n\u003cp\u003ePeripheral nerve damage can also cause trismus, through neuroinflammatory and hyperexcitability mechanisms. Trauma or accidental injury during dental surgery to the trigeminal mandibular division (V3) — for example during nerve blocks or tooth extractions — can disrupt axonal integrity (the nerve fibre's structure) and trigger inflammatory cascades. These release mediators such as bradykinin and adenosine triphosphate, which promote peripheral sensitisation (heightened nerve sensitivity). This works by modulating ion channel activity, in particular increasing T-type calcium channels and hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels in trigeminal ganglion neurons. The result is abnormal neuronal excitability and spontaneous ectopic discharges — nerve firing when it should not.\u003c\/p\u003e\n\n\u003cp\u003eThat abnormal activity travels along motor fibres and causes sustained contraction of the masseter, temporalis, and pterygoid muscles. Direct nerve compression or post-traumatic fibrosis (scarring) can further impair normal inhibitory signalling between opposing jaw muscles, worsening the trismus.\u003c\/p\u003e\n\n\u003cp\u003eThe authors draw a key distinction: central lesions primarily affect supranuclear pathways (above the brainstem motor nuclei), while structural PNS damage shows how localised neuropathic changes — ion channel dysregulation, ectopic firing, and inflammatory fibrosis — can directly generate and sustain trismus.\u003c\/p\u003e\n\n\u003ch2 id=\"neuro-nonstructural\"\u003eNeurological Causes Without Structural Damage\u003c\/h2\u003e\n\n\u003cp\u003eSeveral neurological conditions produce trismus without structural damage, including Parkinson's disease (PD) and atypical parkinsonian syndromes such as progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). In these conditions, dysregulation of the masticatory muscles can promote trismus.\u003c\/p\u003e\n\n\u003cp\u003eTrismus can also be a manifestation of oromandibular dystonia (OMD), particularly the jaw-closing subtype, or in severe cases part of status dystonicus (a life-threatening episode of continuous, severe muscle contraction). Epileptic status, through sustained hyperactivation of cortical and subcortical motor circuits, can precipitate involuntary contraction of the masticatory muscles. Storage diseases, often genetic, are another group — including copper storage disease (Wilson's disease) and iron-related neurodegeneration.\u003c\/p\u003e\n\n\u003cp\u003eMedication adverse effects or poisoning are an important non-structural neurological category and include phenothiazines and metoclopramide. The review also lists malignant syndrome (including neuroleptic malignant syndrome), functional disorders, hemimasticatory spasm, and uremic encephalopathy (brain dysfunction from kidney failure) in this group.\u003c\/p\u003e\n\n\u003cp\u003eTetanus deserves special attention. Tetanus causes involuntary contractions of skeletal muscles, including the masseter and other jaw-closing muscles. Clinically, this produces the characteristic \"lockjaw\" of tetanus, which often appears before the disease's systemic (whole-body) manifestations. The severity and duration of tetanus-related trismus correlate with how much toxin-mediated neuronal inhibition has occurred. Early recognition is critical, because it allows prompt treatment with antitoxin therapy, supportive care, and muscle relaxants. The authors note that tetanus-induced trismus is a useful model for studying toxin-mediated hypertonia in the peripheral nervous system.\u003c\/p\u003e\n\n\u003cp\u003eHeavy metal exposure — particularly lead and mercury — can also cause neurotoxicity that disrupts normal motor neuron function, leading to increased muscle tone and spastic contractions, including in the masticatory muscles. The review also lists trigeminal neuralgia, hypocalcaemia and hypomagnesemia (low blood calcium and magnesium), anaesthetic medications such as succinylcholine, halothane, and etomidate, and muscle contractures among the non-structural causes.\u003c\/p\u003e\n\n\u003cp\u003eThe practical message: when structural brain or nerve lesions have been ruled out, doctors should take a detailed medication and exposure history, use neurophysiological tests (EEG — electroencephalography; EMG — electromyography; and trigeminal reflex testing), and finally evaluate for botulinum toxin exposure. This integrated approach separates organic (drug-induced) causes from functional or psychogenic causes and from tetanus, guiding the right diagnostic and treatment path.\u003c\/p\u003e\n\n\u003ch2 id=\"nonneuro-structural\"\u003eNon-Neurological, Structural Causes\u003c\/h2\u003e\n\n\u003cp\u003eNon-neurological causes cover a broad range of structural and inflammatory conditions that restrict jaw movement through mechanical obstruction, fibrosis, or joint dysfunction.\u003c\/p\u003e\n\n\u003cp\u003eCongenital malformations — conditions present from birth — include trismus pseudo-camptodactyly syndrome and arthrogryposis multiplex congenita. These involve musculoskeletal abnormalities or fibrous contractures that restrict jaw mobility from the outset.\u003c\/p\u003e\n\n\u003cp\u003eTemporomandibular joint disorders are a major non-neurological cause in dental and maxillofacial practice, covering joint dysfunction and ankylosis (stiffening or fusion of the joint).\u003c\/p\u003e\n\n\u003cp\u003eOther structural causes listed by the authors include:\u003c\/p\u003e\n\n\u003cul\u003e\n  \u003cli\u003eTumours of the oral cavity, oropharynx, or the masticator space.\u003c\/li\u003e\n  \u003cli\u003eTrauma, including fractures of the mandible or maxilla.\u003c\/li\u003e\n  \u003cli\u003eOrofacial infections — peritonsillar abscess, dental abscess, and osteomyelitis (bone infection).\u003c\/li\u003e\n  \u003cli\u003ePost-surgical oedema (swelling) or hematoma (blood collection) after dental or maxillofacial procedures, and surgical complications generally.\u003c\/li\u003e\n  \u003cli\u003eSoft tissue injuries causing hematoma or oedema.\u003c\/li\u003e\n  \u003cli\u003eRadiation therapy, and fibrosis due to prolonged immobility.\u003c\/li\u003e\n  \u003cli\u003eBurns.\u003c\/li\u003e\n  \u003cli\u003eComplications of dental extraction, especially an impacted third molar (wisdom tooth).\u003c\/li\u003e\n  \u003cli\u003eRheumatoid arthritis, scleroderma, and temporal arteritis.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2 id=\"nonneuro-nonstructural\"\u003eNon-Neurological, Non-Structural Causes\u003c\/h2\u003e\n\n\u003cp\u003eThis category covers conditions that reduce jaw opening without a structural block or nerve lesion. The authors list myofascial pain syndrome (pain originating in the muscles and connective tissue of the jaw) and malignant hyperthermia — a rare, life-threatening reaction to certain anaesthetic agents characterised by dangerously high body temperature and muscle rigidity. Malignant syndrome appears in this group as well.\u003c\/p\u003e\n\n\u003cp\u003eThe clinical point is that these conditions require a different diagnostic route from structural or neurological causes. They are identified largely through history and examination rather than through imaging alone.\u003c\/p\u003e\n\n\u003ch2 id=\"table\"\u003eFull Differential Diagnosis List\u003c\/h2\u003e\n\n\u003cp\u003eThe review's Table 1 sets out the complete differential diagnosis — the full list of conditions doctors should consider when a patient presents with trismus.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eNeurological causes — central nervous system (structural):\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eTraumatic brain injury (TBI), including diffuse axonal injury (DAI)\u003c\/li\u003e\n  \u003cli\u003eBrain tumours\u003c\/li\u003e\n  \u003cli\u003eStroke (ischemic or haemorrhagic)\u003c\/li\u003e\n  \u003cli\u003eMultiple sclerosis\u003c\/li\u003e\n  \u003cli\u003eCNS infections: meningitis and encephalitis\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cstrong\u003eNeurological causes — peripheral nervous system (structural):\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eTrigeminal nerve lesions\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cstrong\u003eNeurological causes — central nervous system (non-structural):\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eStatus epilepticus\u003c\/li\u003e\n  \u003cli\u003eParkinson's disease and atypical parkinsonian syndromes\u003c\/li\u003e\n  \u003cli\u003eStorage disease (for example, Wilson's disease)\u003c\/li\u003e\n  \u003cli\u003eMedication adverse effects or poisoning (phenothiazines, metoclopramide, and others)\u003c\/li\u003e\n  \u003cli\u003eFunctional disorder\u003c\/li\u003e\n  \u003cli\u003eMalignant syndrome\u003c\/li\u003e\n  \u003cli\u003eStatus dystonicus and oromandibular dystonia (OMD)\u003c\/li\u003e\n  \u003cli\u003eHemimasticatory spasm\u003c\/li\u003e\n  \u003cli\u003eUremic encephalopathy\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cstrong\u003eNeurological causes — peripheral nervous system (non-structural):\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eTetanus\u003c\/li\u003e\n  \u003cli\u003eTrigeminal neuralgia\u003c\/li\u003e\n  \u003cli\u003eHeavy metal poisoning (lead or mercury)\u003c\/li\u003e\n  \u003cli\u003eHypocalcaemia, hypomagnesemia\u003c\/li\u003e\n  \u003cli\u003eAnaesthetic medications (succinylcholine, halothane, etomidate)\u003c\/li\u003e\n  \u003cli\u003eMuscle contractures\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cstrong\u003eNon-neurological causes (structural and non-structural):\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eTMJ disorders (dysfunction or ankylosis)\u003c\/li\u003e\n  \u003cli\u003eTumours of the oral cavity or oropharynx, or of the masticator space\u003c\/li\u003e\n  \u003cli\u003eTrauma\u003c\/li\u003e\n  \u003cli\u003eOrofacial infections (peritonsillar abscess, dental abscess, osteomyelitis)\u003c\/li\u003e\n  \u003cli\u003eFractures of the mandible or maxilla\u003c\/li\u003e\n  \u003cli\u003ePost-surgical oedema or hematoma following dental or maxillofacial procedures\u003c\/li\u003e\n  \u003cli\u003eSurgical complications\u003c\/li\u003e\n  \u003cli\u003eSoft tissue injuries causing hematoma or oedema\u003c\/li\u003e\n  \u003cli\u003eRadiation therapy\u003c\/li\u003e\n  \u003cli\u003eFibrosis due to prolonged immobility\u003c\/li\u003e\n  \u003cli\u003eBurns\u003c\/li\u003e\n  \u003cli\u003eComplication of dental extraction (impacted third molar)\u003c\/li\u003e\n  \u003cli\u003eRheumatoid arthritis\u003c\/li\u003e\n  \u003cli\u003eScleroderma\u003c\/li\u003e\n  \u003cli\u003eTemporal arteritis\u003c\/li\u003e\n  \u003cli\u003eCongenital malformation: trismus pseudo-camptodactyly syndrome, arthrogryposis multiplex congenita\u003c\/li\u003e\n  \u003cli\u003eMyofascial pain syndrome\u003c\/li\u003e\n  \u003cli\u003eMalignant hyperthermia\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2 id=\"diagnosis\"\u003eDiagnosis: How Doctors Tell These Causes Apart\u003c\/h2\u003e\n\n\u003cp\u003eDiagnosis of trismus is primarily based on clinical assessment and physical examination. Instrumental investigations then help identify the underlying etiology (cause).\u003c\/p\u003e\n\n\u003cp\u003eThe authors emphasise that a thorough clinical evaluation should be combined with two kinds of testing. The first is neuroimaging — MRI and CT scans — to look for structural lesions. The second is neurophysiological testing that targets the trigeminal nerve, such as trigeminal reflex studies. Together, these help accurately define the mechanism behind the trismus, improve diagnostic precision, and guide individualised treatment.\u003c\/p\u003e\n\n\u003cp\u003eWhen structural lesions of the CNS or PNS have been excluded, a further sequence is recommended:\u003c\/p\u003e\n\n\u003col\u003e\n  \u003cli\u003eTake a detailed anamnestic history (the patient's full medical and medication history) and pharmacological history.\u003c\/li\u003e\n  \u003cli\u003ePerform neurophysiological investigations — EEG, EMG, and trigeminal reflex testing.\u003c\/li\u003e\n  \u003cli\u003eEvaluate for botulinum toxin exposure.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003cp\u003eThis integrated approach lets doctors separate organic (drug-induced) causes from functional or psychogenic causes and from tetanus-induced trismus, and then choose the right diagnostic and treatment strategy.\u003c\/p\u003e\n\n\u003cp\u003eThe authors also flag a practical problem in diagnosis: it is difficult to distinguish trismus from other causes of limited mouth opening, particularly in sedated or critically ill patients. That is why their algorithm prioritises red flag conditions — urgent, potentially life-threatening causes that must be identified and treated quickly.\u003c\/p\u003e\n\n\u003ch2 id=\"treatment\"\u003eTreatment Approaches Covered by the Review\u003c\/h2\u003e\n\n\u003cp\u003eThe authors propose a stepwise diagnostic and management algorithm. It prioritises red flag conditions, guides differential diagnosis, and supports treatment decisions in both outpatient and hospital settings — including surgical and critical care considerations.\u003c\/p\u003e\n\n\u003cp\u003eThe treatment approaches assessed in the reviewed literature include:\u003c\/p\u003e\n\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePharmacological therapy\u003c\/strong\u003e (medication).\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBotulinum toxin type A (BoNT-A)\u003c\/strong\u003e — a purified bacterial toxin given in very small doses to relax overactive muscles. BoNT-A appears in the article's keyword list and was a dedicated search term in the review.\u003c\/li\u003e\n  \u003cli\u003e\u003cstrong\u003ePhysical therapy.\u003c\/strong\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003cstrong\u003eSurgical procedures.\u003c\/strong\u003e\u003c\/li\u003e\n  \u003cli\u003e\u003cstrong\u003eRehabilitation strategies.\u003c\/strong\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eFor tetanus specifically, the review notes that early recognition is critical because it enables prompt treatment with antitoxin therapy, supportive care, and muscle relaxants. The severity and duration of tetanus-related trismus track with the extent of toxin-mediated neuronal inhibition, which is why speed matters.\u003c\/p\u003e\n\n\u003cp\u003eThe authors frame the whole algorithm around one aim: matching the treatment to the mechanism. A patient whose trismus comes from an overactive jaw-closing muscle after corticobulbar damage is not treated the same way as a patient with a dental abscess, a tetanus infection, or a drug reaction.\u003c\/p\u003e\n\n\u003ch2 id=\"implications\"\u003eWhat This Means for Patients\u003c\/h2\u003e\n\n\u003cp\u003eThe most important message is that trismus is a symptom, not a diagnosis. It is a sign that something is wrong with the chewing system, and the underlying cause could range from a minor dental problem to a neurological emergency.\u003c\/p\u003e\n\n\u003cp\u003eBecause prevalence data are lacking and screening is not standardised, trismus is likely under-recognised. Patients who notice they cannot open their mouth as widely as before — especially if the change is persistent or worsening — should treat it as a reason to seek medical assessment, not something to wait out.\u003c\/p\u003e\n\n\u003cp\u003eThe new classification matters to patients because it gives clinicians a structured route to the right answer. Neurological versus non-neurological, structural versus non-structural — this framework prompts the right questions, the right imaging, and the right referrals. In practice, that means fewer patients being treated for the wrong cause.\u003c\/p\u003e\n\n\u003cp\u003eIt also means treatment can be targeted. If the problem is a structural block such as an abscess or a fractured jaw, the solution is structural. If the problem is a hyperactive nerve pathway, the solution may involve medication or botulinum toxin. If the problem is tetanus, the priority is antitoxin therapy and intensive support.\u003c\/p\u003e\n\n\u003ch2 id=\"limitations\"\u003eLimitations of This Review\u003c\/h2\u003e\n\n\u003cp\u003eSeveral limitations deserve honest acknowledgement.\u003c\/p\u003e\n\n\u003cul\u003e\n  \u003cli\u003eThis is a narrative review, not a systematic review. The authors state this explicitly. The inclusion and exclusion criteria were used as a guide, not as a rigid filter, and the authors deliberately included some highly cited or clinically significant papers that did not meet every criterion.\u003c\/li\u003e\n  \u003cli\u003eBecause it is non-systematic, the selection of studies involves judgement. Different reviewers might have chosen different papers.\u003c\/li\u003e\n  \u003cli\u003eThe prevalence of trismus remains uncertain. There are no standardised screening protocols, so nobody knows exactly how many people are affected or how the numbers break down by cause.\u003c\/li\u003e\n  \u003cli\u003eTrismus is often under-estimated, especially in sedated or critically ill patients who cannot report symptoms reliably.\u003c\/li\u003e\n  \u003cli\u003eThe proposed classification and the stepwise algorithm are new proposals from the authors. The review does not report that they have been validated in prospective clinical trials — the article describes a framework, not a tested protocol with outcome data.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eNone of this makes the framework useless. It means the framework should be read as expert synthesis and a practical guide, not as proof of superiority over existing approaches.\u003c\/p\u003e\n\n\u003ch2 id=\"recommendations\"\u003ePractical Recommendations\u003c\/h2\u003e\n\n\u003cp\u003eBased on the review, the following practical points apply to patients and the clinicians caring for them.\u003c\/p\u003e\n\n\u003col\u003e\n  \u003cli\u003e\n\u003cstrong\u003eTreat reduced mouth opening as a clinical sign, not a nuisance.\u003c\/strong\u003e If you cannot open your mouth as widely as usual, and the change persists, get assessed.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eKnow the red flags.\u003c\/strong\u003e Rapidly worsening jaw closure, fever, facial swelling, recent dental surgery or trauma, recent tetanus exposure, or a new medication start should prompt urgent evaluation.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBring a full medication list.\u003c\/strong\u003e Drug-induced trismus is a real category — phenothiazines, metoclopramide, and anaesthetic agents such as succinylcholine, halothane, and etomidate are all listed. So are lead and mercury exposure.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eReport recent procedures.\u003c\/strong\u003e Dental extractions (especially impacted wisdom teeth), nerve blocks, and maxillofacial surgery are recognised triggers.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eExpect imaging and nerve testing.\u003c\/strong\u003e MRI, CT, EEG, EMG, and trigeminal reflex studies may be used to find the cause.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eAsk whether botulinum toxin type A is appropriate.\u003c\/strong\u003e BoNT-A is one of the treatment options reviewed for trismus.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFollow through with rehabilitation and physical therapy.\u003c\/strong\u003e Prolonged immobility itself causes fibrosis, so keeping the jaw moving under professional guidance matters.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eIf tetanus is suspected, act immediately.\u003c\/strong\u003e Early recognition allows antitoxin therapy, supportive care, and muscle relaxants — the earlier, the better.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003c!-- ddn:faq:start --\u003e\n\u003ch2 id=\"ddn-faq\"\u003eFrequently Asked Questions\u003c\/h2\u003e\n\u003ch3\u003eWhat is trismus, or lockjaw?\u003c\/h3\u003e\n\u003cp\u003eTrismus, commonly called lockjaw, is a condition in which a person cannot fully open their mouth because the chewing muscles stay tightly contracted. The restriction is persistent and involuntary, caused by sustained tightening or spasm of the masticatory muscles. It is a symptom, not a diagnosis, meaning an underlying cause should be identified. It is often under-recognised, especially in sedated or critically ill patients who cannot report symptoms.\u003c\/p\u003e\n\u003ch3\u003eWhat causes trismus?\u003c\/h3\u003e\n\u003cp\u003eCauses are split into neurological and non-neurological, then structural and non-structural. Neurological causes include stroke, traumatic brain injury, Parkinson's disease, tetanus, medication effects, and heavy metal poisoning. Non-neurological structural causes include temporomandibular joint disorders, tumours, trauma, infections, radiation therapy, and dental extraction complications. Non-neurological non-structural causes include myofascial pain syndrome and malignant hyperthermia. A full medication and exposure history helps separate these categories.\u003c\/p\u003e\n\u003ch3\u003eHow do doctors diagnose trismus?\u003c\/h3\u003e\n\u003cp\u003eDiagnosis is primarily based on clinical assessment and physical examination, combined with instrumental tests. Doctors may use MRI and CT scans to look for structural lesions, and neurophysiological testing targeting the trigeminal nerve, such as trigeminal reflex studies. If structural lesions are excluded, they take a detailed medical and medication history, perform EEG, EMG, and trigeminal reflex testing, and evaluate for botulinum toxin exposure. This separates drug-induced, functional, and tetanus-related causes.\u003c\/p\u003e\n\u003ch3\u003eWhat treatments are available for trismus?\u003c\/h3\u003e\n\u003cp\u003eTreatment approaches reviewed include pharmacological therapy, botulinum toxin type A (BoNT-A), physical therapy, surgical procedures, and rehabilitation strategies. For tetanus specifically, early recognition is critical because it allows prompt treatment with antitoxin therapy, supportive care, and muscle relaxants. The aim is to match treatment to the underlying mechanism, so a patient with an overactive jaw-closing muscle is not treated the same way as one with a dental abscess or a drug reaction.\u003c\/p\u003e\n\u003ch3\u003eWhen should I seek urgent care for lockjaw?\u003c\/h3\u003e\n\u003cp\u003eSeek urgent evaluation for rapidly worsening jaw closure, fever, facial swelling, recent dental surgery or trauma, recent tetanus exposure, or a new medication start. These are red flag features that may indicate urgent, potentially life-threatening causes. If tetanus is suspected, act immediately, because early recognition allows antitoxin therapy, supportive care, and muscle relaxants. Reduced mouth opening that is persistent or worsening should be assessed rather than waited out.\u003c\/p\u003e\n\u003ch3\u003eWhat should I bring to my appointment for trismus?\u003c\/h3\u003e\n\u003cp\u003eBring a full medication list, because drug-induced trismus is a real category. Phenothiazines, metoclopramide, and anaesthetic agents such as succinylcholine, halothane, and etomidate are listed, as are lead and mercury exposure. Also report recent procedures: dental extractions, especially impacted wisdom teeth, nerve blocks, and maxillofacial surgery are recognised triggers. Expect that imaging and nerve testing may be used to find the cause.\u003c\/p\u003e\n\u003ch3\u003eWhen should a patient with lockjaw (trismus) seek a second opinion?\u003c\/h3\u003e\n\u003cp\u003eTrismus is a symptom, not a diagnosis, and its causes range from a dental abscess to a neurological emergency, so the underlying reason matters more than the jaw restriction itself. A second opinion is reasonable when no clear cause has been identified, when structural brain or nerve lesions have been excluded but symptoms persist, or when the proposed treatment does not match the suspected mechanism. Because the classification and stepwise algorithm are new proposals not yet validated in prospective trials, an independent review of the diagnosis and records can help confirm the cause. Diagnostic Detectives Network provides independent expert second opinions.\u003c\/p\u003e\n\u003c!-- ddn:faq:end --\u003e\n\n\u003ch2 id=\"source\"\u003eSource Information\u003c\/h2\u003e\n\n\u003cp\u003e\u003cstrong\u003eOriginal article title:\u003c\/strong\u003e An update on trismus: etiology, diagnosis and treatment.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eAuthors:\u003c\/strong\u003e Falletti M, Cuccarelli M, Evangelisti E, Zampogna A, Patera M, Truini A, Romeo U, Suppa A.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eAffiliations:\u003c\/strong\u003e Department of Human Neurosciences, Sapienza University of Rome, Rome, Italy; Department of Anesthesia and Intensive Care Unit, Campus Bio-Medico University Hospital Foundation, Rome, Italy; IRCCS Neuromed Institute, Pozzilli, Italy; Department of Oral and Maxillofacial Sciences, Sapienza University of Rome, Rome, Italy.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eJournal:\u003c\/strong\u003e Frontiers in Neurology, volume 17, article 1758417.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eDOI:\u003c\/strong\u003e 10.3389\/fneur.2026.1758417\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003ePublication timeline:\u003c\/strong\u003e Received 1 December 2025; revised 27 February 2026; accepted 10 March 2026; published 24 March 2026; corrected 20 April 2026.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eArticle type:\u003c\/strong\u003e Review (narrative, non-systematic). Open access under a Creative Commons Attribution License (CC BY).\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eKeywords:\u003c\/strong\u003e botulin toxin, lockjaw, malignant syndrome, tetanus, trismus.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eEditors and reviewers:\u003c\/strong\u003e Edited by Gabriele Siciliano (University of Pisa, Italy). Reviewed by Farzin Sarkarat (Gulf Medical University, United Arab Emirates) and Daiana Cristina Pereira Santana (Federal University of Bahia, Brazil).\u003c\/p\u003e\n\n\u003cp\u003e\u003cem\u003eThis patient-friendly article is based on peer-reviewed research. It is intended for educational purposes and does not replace personalised medical advice. If you or someone you care for has trouble opening the mouth, speak to a qualified clinician.\u003c\/em\u003e\u003c\/p\u003e","brand":"DiagnosticDetectives.Com","offers":[{"title":"Default Title","offer_id":47738999079068,"sku":null,"price":0.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0599\/5449\/5644\/files\/ddn-medical-article-lockjaw-trismus-a-complete-guide-to-causes-diagnosis-and-treatment-hero.png?v=1791782480","url":"https:\/\/diagnosticdetectives.com\/zh\/products\/lockjaw-trismus-a-complete-guide-to-causes-diagnosis-and-treatment","provider":"DiagnosticDetectives.Com","version":"1.0","type":"link"}