What can cause sudden onset lockjaw (trismus)?

Sudden Onset Lockjaw (Trismus): Causes and Evaluation

Sudden onset lockjaw (trismus) most commonly results from infection (dental abscess, peritonsillar abscess), trauma to the jaw or temporomandibular joint, tumor invasion into muscles of mastication, or medication-induced acute dystonia—with tetanus being a critical life-threatening cause that must be excluded immediately based on vaccination history and clinical presentation. 1, 2

Life-Threatening Causes Requiring Immediate Exclusion

Tetanus

• Tetanus presents with sustained tonic spasm of jaw muscles (the original definition of trismus) and requires urgent assessment of vaccination status, wound history, and presence of generalized muscle rigidity. 1
• Look for progression to generalized muscle spasms, opisthotonus, and autonomic instability. 1

Airway Compromise

• Assess vital signs immediately to ensure no laryngeal involvement, particularly in medication-induced dystonia cases where airway obstruction can develop rapidly. 3
• Evaluate for stridor, respiratory distress, or difficulty swallowing. 3

Common Infectious Causes

Odontogenic Infection

• Dental abscess is one of the most frequent causes of trismus, presenting with localized pain, swelling, and fever. 1, 2
• Examine for carious teeth, gingival swelling, fluctuance, and regional lymphadenopathy. 1

Deep Space Infections

• Peritonsillar abscess, parapharyngeal abscess, or masticator space infections cause trismus through direct muscle involvement or inflammatory edema. 1, 2
• Look for fever, dysphagia, muffled voice, and asymmetric pharyngeal swelling. 1

Malignancy-Related Trismus

Tumor Invasion

• Trismus may manifest tumor invasion into muscles of mastication, especially the medial pterygoid muscle, which would be a contraindication to surgical approaches and indicates advanced disease. 4
• Oropharyngeal squamous cell carcinoma, particularly involving the tonsillar fossa or base of tongue, can present with progressive trismus. 4
• In pediatric patients, severe trismus with systemic symptoms (fatigue, icteric appearance, lymphadenopathy) may indicate acute lymphoblastic leukemia from infiltration of leukemic cells into facial muscles. 5

Imaging Evaluation

• When tumor invasion is suspected, CT or MRI is essential to evaluate extent of disease and involvement of pterygoid muscles. 4
• Trismus from facial trauma requires imaging to exclude mandibular fractures, particularly when accompanied by malocclusion, gingival hemorrhage, or visible deformity. 4

Medication-Induced Acute Dystonia

Drug-Induced Trismus

• Antipsychotics are the classic culprits, but antidepressants (particularly duloxetine) can cause isolated trismus as an acute dystonic reaction within days of initiation. 3
• Patients present with sudden jaw stiffness, difficulty opening mouth and speaking, without other neurological deficits. 3
• Treatment requires immediate intravenous anticholinergics (procyclidine or benztropine) combined with oral benzodiazepines, with rapid symptom resolution confirming the diagnosis. 3

Local Anesthetic Reaction

• Trismus following mandibular block anesthesia can occur from direct muscle trauma, hematoma formation, or local anesthetic myotoxicity. 5, 2
• Onset is typically within hours to days of the dental procedure. 2

Post-Treatment Causes

Radiation-Induced Fibrosis

• Trismus may be a manifestation of fibrosis from previous radiation therapy to the head and neck, developing months to years after treatment. 4
• Distinguish from tumor recurrence through imaging and clinical examination. 4

Post-Chemotherapy

• Chemotherapy can cause trismus through mucositis, secondary infection, or direct muscle effects. 5

Temporomandibular Joint Disorders

TMJ Pathology

• Trismus may manifest from temporomandibular joint disease, presenting with chronic or acute-on-chronic limitation of jaw opening, joint clicking, and pain with jaw movement. 4
• Differentiate from muscle invasion by absence of mass effect and presence of joint-specific symptoms. 4

Critical Diagnostic Algorithm

1. Assess airway and vital signs immediately 3
2. Obtain vaccination history to exclude tetanus 1
3. Examine for infection: dental, pharyngeal, or deep space 1, 2
4. Review medication list for recent antipsychotics or antidepressants 3
5. Evaluate for trauma history and facial bone integrity 4
6. In patients with cancer history or risk factors, image to exclude tumor invasion 4
7. In pediatric patients with systemic symptoms, obtain complete blood count 5

Common Pitfalls to Avoid

• Do not assume all trismus is benign TMJ dysfunction—always exclude infection, malignancy, and tetanus first. 1, 2
• In patients over 50 with facial pain and trismus, consider giant cell arteritis with jaw claudication, which requires urgent high-dose corticosteroids to prevent blindness. 6
• Trismus with facial nerve palsy suggests different pathology (parotid tumor, skull base lesion) and requires comprehensive cranial nerve examination. 4
• Bilateral trismus is atypical for most focal causes and should prompt consideration of systemic disease, tetanus, or medication effect. 7, 1