Maxfacts

With many different possible causes of trismus, and widely varying degrees of severity and duration in mind, we look in a little more detail and a little more systematically at the overall picture of this condition.

Causes for trismus can roughly be divided into those internal to the jaw joint (the temporomandibular joint, TMJ), and those external to the joint.

Intra-articular (internal to the jaw joint) causes for trismus

The jaw joint itself can be affected by inflammation from autoimmune conditions such as (rheumatoid) arthritis. Ankylosis, the fusing of bones in the joint, can be another consequence of inflammation in the joint. The connective tissue of the articular disk (the meniscus) of the temporomandibular joint normally provides the gliding surface for smooth movement of the jaw. This surface tissue can either be degraded by degenerative conditions such as arthritis or ankylosis, or may suffer some displacement from trauma. The latter is the most common intra-articular cause for trismus. All of these conditions lead to variable degrees of trismus and require exact diagnosis and assessment for treatment planning.

Extra-articular (external to the jaw joint) causes for trismus

Of the many different extra-articular causes of trismus, some are very common and mainly cause short-term temporary difficulties with opening of the mouth and/or movements of the jaw in general.

Infection

These can be odontogenic (dental) pulpal (soft centre of a tooth), periodontal (gum) or pericoronal (soft tissue surrounding erupting teeth) infections. Non-odontogenic infections include tonsillitis and tonsillar abscess, meningitis, mumps, tetanus (nowadays very rare, at least in the rich western countries) and a range of abscesses afflicting the parotid gland or the base of the skull, as well as infections of the jaw bones (for example, acute osteomyelitis).

Trauma

Fractures of the mandible (lower jaw) and the zygomatic arch (cheek bone) are common causes of trismus. Rare traumatic conditions causing scarring of the oral mucosa (lining of the mouth) may cause trismus.

Dental and surgical treatment

The two most common causes of trismus related to dental treatments are the extraction of teeth (in particular the extraction of mandibular third molars (wisdom teeth)) and local anaesthetic injections (which may sometimes cause a minor bleed and give rise to a haematoma).

Temporomandibular (jaw) joint disorders

These are common conditions that may be caused by trauma to the jaw joint (for example, prolonged and particularly wide opening of the mouth) or by painful spasms of the muscles that move the jaws (myofascial pain dysfunction syndrome).

Tumours

In particular tumours affecting the pharynx (back of the throat), the parotid gland (salivary gland), the jaws or jaw joints can all cause trismus. A pre-malignant condition common in the Indian subcontinent and related to chewing of betel nuts is submucous fibrosis, an extreme form of scarring of the submucosal tissue in the mouth leading to difficulties with tongue and jaw movements. Any tumour which invades the muscles of mastication (muscles that enable chewing) can cause trismus; this includes the hard to identify tumours of the infratemporal fossa (cavity near the cheekbone).

Radiotherapy

Radiotherapy plays a role in the treatment of many head and neck malignancies. It can cause necrosis of the jaw bones, osteoradionecrosis, and soft tissues in the head and neck region, depending on radiation dose. Trismus can occur as another (late on-set) side effect when the body’s attempts to heal radiation damage in the jaw muscles leads to extensive fibrosis (scarring) of the muscle tissue such that it becomes impossible to move the jaw and to open the mouth.

Drugs

A number of antipsychotic drugs (including fairly commonly prescribed tricyclic antidepressants (fluoxetine) and phenothiazines), some muscle-relaxing agents used in general anaesthesia (succinyl choline, halothane) and metoclopramide (medication used to treat nausea and other stomach problems, including heartburn), amongst others, can cause trismus in different ways. Many chemotherapy drugs cause stomatitis and mucositis (painful inflammation of the soft tissues in the mouth), often severe enough to lead to trismus.

Congenital (inborn)

If somebody is born with Möbius syndrome, a hypertrophy of the coronoid (a part of the mandible), they have an enlarged part of the mandible that will hinder movement of the jaws, at birth or later in life. Some rare hereditary conditions can also lead to malformations and malfunctions, for example short tendons of facial (and other) muscles and cause trismus (trismus pseudocamptodactyly syndrome).

Other causes

Scleroderma, an autoimmune condition that leads to hardening of the skin can cause trismus if facial skin is affected. Lupus erythematosus, another autoimmune disease, can cause mouth ulcers as well as trismus from painful jaw joints. There can by psychogenic causes for trismus (an old-fashioned term for the effect is hysteria): extreme psychological and emotional distress can sometimes be translated to physical symptoms, with trismus being one these.