Trismus

Etiology

Multiple conditions can result in trismus. Acute trismus may be caused by facial, mandibular, or iatrogenic trauma. Examples of iatrogenic trauma include third molar extraction and intramuscular administration of anesthesia.[3] Acute trismus from iatrogenic causes tends to be self-limiting.[3] Severe trauma usually causes chronic trismus.[3] Chronic trismus may arise from temporomandibular disorders, neoplasia, surgery, radiotherapy in the head and neck for managing cancer, local infections, and connective tissue disorders like lupus erythematosus.[3]

Trismus As a Complication of Local Anesthesia

Trismus is a possible complication of the inferior alveolar nerve block. During the administration of this block, the masticatory muscles, mainly the medial pterygoid muscle, can be accidentally penetrated, resulting in pain-related trismus. When the affected muscle stretches, it triggers pain, causing immediate reflex contraction and mandibular opening limitation.[4] Trismus may also arise when an intramuscular hematoma occurs.[4] Injury to the inferior alveolar artery or vein may lead to hematoma in the pterygomandibular space, resulting in trismus.[4] Trismus after 2 to 3 days of the injection is most likely caused by a needle-track infection.[4]

Trismus As a Complication of Dental Extractions

Pain, trismus, and swelling are common complications of the surgical extraction of mandibular third molars.[5] Such complications result from the inflammatory response to surgical trauma and are classically short-term.[5][6][5]

Trismus As a complication of Trauma to the Face and Mandible

Fractures, mainly mandibular, may result in limited mouth opening.[1] Although rare, fractures of the zygomatic arch and zygomaticomaxillary complex can cause trismus as they impede the movement of the coronoid process.[1]

Trismus As a sign Of Temporomandibular Disorders (TMD)

Temporomandibular disorders refer to the dysfunction and pain of the mastication's temporomandibular joint (TMJ) and muscles.[7] TMDs typically cause facial and preauricular pain, functional noises in the TMJ, and limitation in mandibular movement.[7] Therefore, many patients reporting limited mouth opening likely have a TMD. Myofascial pain and disc displacement without reduction are 2 common types of TMD that may cause trismus.[8]

Trismus As a Complication of Dental Infection

Dental infection must be suspected in patients with acute trismus, as severe dental infections involving the masticatory muscles often cause trismus.[9] These infections can extend into the head and neck spaces and result in life-threatening complications, like mediastinitis and cervical cellulitis.[1] From the infections of dental origin, pericoronitis is more associated with trismus.[1] Examples of infections from non-odontogenic sources that may trigger trismus include tonsillitis, parotid abscess, tetanus, meningitis, and brain abscess.[1]

Trismus as a Sign of Malignancy

Patients with limited mouth opening and pain in the pre-auricular area are likely to be diagnosed with TMD.[10] However, although less common, trismus may also be caused by malignancy.

Trismus rarely presents as the primary sign of malignancy, but it should not be ruled out. Cases of misdiagnosis of trismus as TMD leading to delayed diagnosis of malignancy have been described in the literature. For example, a case of a 62-year-old patient presenting with severe trismus and TMJ pain was misdiagnosed as having a TMD and underwent treatment but was found to have adenocarcinoma of the temporal region a year later.[10] For this reason, a specialist TMD clinic has developed a checklist to identify trismus cases with atypical features.[8] If a patient presents with the following 5 signs and symptoms, radiographs and referral to a senior clinician must be considered.[8]

1. Opening less than 15 mm
2. No history of clicking
3. Pain of non-myofascial origin (eg, neuralgia)
4. Lymphadenopathy
5. Suspicious intra-oral soft tissue lesion

Trismus As a Complication Of Head and Neck Cancer Treatment

Trismus is a common side effect of head and neck cancer and its treatment.[11] According to recent studies, it develops in 38% to 42% of head and neck cancer patients.[12][13] The TMJ or the mastication muscles can experience fibrosis because of radiotherapy, leading to trismus.[11] The trismus risk increases when the medial pterygoid muscle is in the radiation zone.[14] Furthermore, surgical procedures to treat head and neck cancer can scar the mastication muscles and restrict mandibular opening.[15]

Classification

Multiple conditions can result in trismus. Some authors classify trismus according to the involvement of the TMJ in intraarticular and extraarticular etiologies.[2] Others have categorized the causes, such as infectious, traumatic, and neoplastic sources.[1] Trismus may also be iatrogenic, resulting from prescribed interventions and treatments. Below are some of the conditions associated with trismus:

Traumatic

• Hemarthrosis/hematoma
• Fracture or dislocation of the mandible or zygomatic arch
• TMJ contusion
• Intraarticular bone islands/foreign bodies
• Displaced meniscus
• Direct injury to muscles of mastication

Inflammatory

• Osteoarthritis
• Soft tissue fibrosis
• TMJ ankylosis
• Rheumatoid arthritis
• Scleroderma
• Temporal arteritis

Infectious

• Pyogenic arthritis
• Osteomyelitis of the mandible
• Tonsillitis
• Peritonsillar or other pharyngeal abscesses
• Tetanus
• Odontogenic abscess
• Mumps
• Parotid abscess

Congenital Malformations

• Pierre-Robin sequence         
• Trismus-pseudocamptodactyly syndrome

Head and Neck Neoplasms

• Pharyngeal carcinoma
• Parotid gland tumors

Odontogenic

• Impacted third molar (or following extraction thereof)

Iatrogenic

• Perioperative inflammation
• Radiotherapy for head and neck cancer

Neurogenic

• Tetanus
• Status epilepticus
• Parkinsonism
• Strychnine, phenothiazine poisoning
• Medication adverse effects (phenothiazines, metoclopramide, tricyclic antidepressants)
• Hypocalcemia, hypomagnesemia, respiratory alkalosis

Psychogenic (conversion disorder)

Epidemiology

The prevalence of trismus ranges widely, partly because no clear criteria have been established, and depends on the inciting etiology. Importantly, trismus is a common finding in certain patient populations, such as those with congenital micrognathia syndromes or undergoing radiation therapy for head and neck cancers.[16][17] It can also be a rare complication of common conditions, such as pharyngitis.

History and Physical

Normal mouth opening ranges between 40 to 60 cm (2 to 3 finger breadths), and many authors consider a maximum mouth opening of less than 35 mm trismus.[1] However, it varies from individual to individual, and even according to sex, males generally feature a wider mouth opening.[1] Patients presenting with trismus note a restricted mouth opening and sometimes pain when attempting to open the mouth. However, patients often complain about the causative condition rather than the resulting trismus. Those with odontogenic etiologies may complain of tooth or gum pain and swelling; patients with traumatic causes may note facial or mandibular pain. A complete clinical examination should be performed to identify systemic causes. Fever may indicate an infectious source; weight loss may be notable among patients with neoplastic causes; carpopedal spasms and paresthesias may accompany trismus in patients with neurogenic or metabolic causes. A history of tobacco use or known cancer could raise suspicion of a neoplastic cause.[1]

During a physical exam, a Trismus may also be encountered when attempting to visualize the oral and pharyngeal structures. This challenges the examining clinician's attempt to ascertain the cause of trismus. The exam should be targeted as much as possible to the teeth and gums, facial bones and TMJ, pharyngeal pillars, tonsils, uvula, and neck. Assessment of the patient's speech may be necessary; some pharyngeal infections implicated in trismus may also cause changes in the patient's voice; a "hot potato voice" may be associated with tonsillitis or peritonsillar abscess. A directed neurologic exam should be performed to evaluate for neurogenic causes.[2]

Evaluation

The diagnosis of trismus is mainly clinical. Imaging adjuncts may be useful in determining its etiology and the TMJ's articular involvement. Computed tomography can help to identify traumatic etiologies, including hematomas or facial and mandibular fractures. Magnetic resonance imaging may identify space-occupying lesions or abnormalities in the pharyngeal or oral structures.

Treatment / Management

Treatment of trismus is directed at the inciting etiology and is most commonly managed symptomatically. Symptom-directed interventions, including heat therapy, analgesics such as non-steroidal anti-inflammatories (NSAIDs), and muscle relaxants, are usually prescribed in the acute phase and are the mainstays for treating uncomplicated transient trismus. Heat therapy includes applying moist hot towels for 15 to 20 min per hour.[1] When it comes to analgesics, aspirin is usually sufficient.[1] When a muscle relaxant is needed, a benzodiazepine, such as diazepam, is recommended with a dose of 2.5 to 5 mg 3 times per day.[1] The clinician should also encourage a soft diet for the duration of the pathology.[1] Further dental treatment must be avoided until the trismus resolves,[18] usually within 48 hours of initiating treatment.

Stretching exercises may be indicated after the acute phase or in patients with post-traumatic and post-operative trismus, particularly when persisting longer than 1 week. The exercises typically involve repeated attempts to open the mouth against applied resistance, usually divided into multiple daily sessions.[11] Physiotherapy includes opening and closing the mouth and lateral movements for 5 min every 3 to 4 hours.[19] Sugar-free chewing gum can be indicated to stimulate lateral movements.[1] Physical therapy alleviates edema and fibrosis, restores blood circulation, improves range of motion and muscle strength, and keeps the muscle active.[3](A1)

Trismus may become chronic in the setting of fibrosis or ongoing radiotherapy. These cases may benefit from intensive physiotherapy, sometimes utilizing commercially available jaw motion rehabilitation devices or microcurrent therapy, particularly in patients refractory to more conservative approaches. Some authors have also described treatment with xanthine derivatives such as pentoxifylline.[1][20]. If trismus does not improve after 2 to 3 days, or in cases of extreme trismus, referral to an oral and maxillofacial surgeon should be considered.[1] Extreme trismus cases that are repeatedly refractory to treatment require surgical procedures, like reducing the mandibular height to achieve a larger mouth opening, coronoidectomy, or tissue release and free flap reconstruction.[11](A1)

The treatment of trismus is summarized in the table below.[1][11][1](A1)

Differential Diagnosis

Since trismus has been defined as a restriction in mouth opening regardless of etiology, it does not have a wide differential diagnosis. Some authors have argued that "true trismus" is mediated via the trigeminal nerve, and intraarticular causes of impaired mouth opening, such as TMJ ankylosis or fibrosis, should be considered separately.[1] Others have outlined such intraarticular processes as subclassifications of trismus.[20]

Prognosis

Trismus is most commonly self-limited and transient, typically resolving within 2 weeks. However, in certain cases, like patients who develop fibrosis from radiotherapy, the course of trismus may be longer and refractory to conservative treatment.[17]

Complications

Trismus interferes with speaking, eating, and swallowing; it has also been associated with aspiration due to impaired swallowing mechanisms. Intubation via the oropharyngeal route may be impossible in patients with significant trismus, necessitating other approaches such as nasopharyngeal intubation or tracheotomy. When its duration is prolonged, it leads to TMJ fibrosis, necessitating directed therapy.[20]