Trismus and Restricted Mouth Opening

OVERVIEW

Definition

• Trismus classically refers to reduced opening of the jaws caused by spasm of the muscles of mastication (temporalis, masseter, medial pterygoid and lateral pterygoid)
• Trismus may also be used to refer to restricted mouth opening in general
• In the past “lockjaw” has been used as a synonym for both trismus and tetanus
• Trismus is derived from the Greek word trismos meaning “a scream; a grinding, rasping or gnashing”

Trismus may be part of the presenting complaint or an incidental finding complicating management of comorbidity

CAUSES

Muscular spasm

• Tetanus
• Seizure
• Upper motor neuron lesions e.g. stroke, traumatic brain injury
• Stiff person syndrome
• hypocalcemic tetany
• Giant cell arteritis
• Drugs and poisons
  • Suxamthonium-induced masseter spasm
  • Malignant hyperthermia
  • Strychnine poisoning
• Myositis
• Trigeminal neuralgia

Intra-articular causes of restricted mouth opening

• Temporo-mandibular joint (TMJ) dysfunction
• TMJ ankylosis (fibrous or bony)
• TMJ arthritis (infective or non-infective)
• TMJ synovitis
• TMJ meniscal disease
• TMJ foreign body

Other extra-articular causes of restricted mouth opening

• Congenital
  • Congenital deformities
  • Gaucher disease
• Psychogenic
• Iatrogenic
  • Radiation therapy to head and neck
• Neoplastic
  • Oral submucous fibrosis
  • Nasopharyngeal or infratemporal tumors/ fibrosis of temporalis tendon
• Infection
  • Orodental infection
  • Malignant otitis externa
  • Peritonsilar abscess
  • Retropharyngeal or parapharyngeal abscess
  • Osteomyelitis
  • Meningitis
  • Cerebral abscess
  • Parotid abscess
• Trauma
  • Severe soft tissue swelling and haematomas
  • Fractures e.g. mandibular condyle, zygomatic arch
• Iatrogenic
  • post-surgical deformity (e.g. temporalis scarring after craniotomy)
  • Wired jaw
  • needle injury to medial pterygoid, local anaesthetic injection in infrapterygoind space)
  • Cervical spine collar preventing mouth opening
• Other
  • Scleroderma
  • Acquired deformity e.g. burns
  • Neck flexion deformity

CLINICAL FEATURES

Restricted mouth opening

• “3 finger test” — functionally normal mouth opening can be assumed if the patient can fit 3 fingers side-by-side between the top and bottom incisors
• <4 cm inter-incisor gap — associated with difficult direct laryngoscopy and orotracheal intubation

Features of underlying cause

• Muscular spasm: pain, tenderness, affected muscles firm to palpation

Complications

• Difficult airway management
• Impaired oral intake, mastication and nutrition
• Poor oral hygiene and increased risk of orodental infection
• Impaired speech
• Aspiration

INVESTIGATIONS

• Depend on suspected underlying cause e.g. X-ray/ CT of TMJ +/- facial bones

MANAGEMENT

Trismus can be acutely life-threatening in patients with airway compromise

• May be associated with other space restricting deformities (e.g. protruding teeth, other facial or cervical spine abnormalities)
• May prevent insertion of
  • Oropharyngeal airways
  • Suprglottic airway devices
  • Laryngoscopes and endotracheal tubes

Neuromuscular blockade

• Relieves trismus caused by muscular spasm
• Suxamethonium should be avoided
  • can cause transient trismus/ masseter spasm
  • Can cause hyperkalaemia in neuromuscular disorders (e.g. tetanus)

Options for restricted mouth opening not amenable to neuromuscular blockade

• Mouth opening appliances to allow orotracheal intubation
• Bowen-Jackson laryngoscope (narrow profile blade)
• Video laryngoscopy and bougie (e.g. McGrath Mac blade, C-Mac, Glidescope) (if >20 mm mouth opening)
• Lighted stylet or Bonfils (if available and user familiarity)
• Flexiscope-assisted nasal intubation (f <20mm mouth opening)
• Blind nasal intubation (risk of bleeding and failure)
• Submental intubation
• Tracheostomy or (in an emergency) cricothyroidotomy

Seek and treat underlying cause and complications

• Depending on the cause, muscular spasm may respond to heat packs, massage, physiotherapy and mouth opening appliances
• Refractory chronic trismus may require physiotherapy interventions

Supportive care and monitoring

Disposition

• Depends on underlying cause and presence or absence of complications

References and Links

Journal articles

• Dhanrajani PJ, Jonaidel O. Trismus: aetiology, differential diagnosis and treatment. Dent Update. 2002 Mar;29(2):88-92, 94. [pubmed]
• O’leary MR. Trismus: modern pathophysiological correlates. Am J Emerg Med. 1990;8(3):220-7. [pubmed]
• Santiago-Rosado LM, Lewison CS. Trismus. 2018 Mar 29. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2018 Jan-. Available from http://www.ncbi.nlm.nih.gov/books/NBK493203/ [pubmed]
• van der Spek AF, Reynolds PI, Fang WB, et al. Changes in resistance to mouth opening induced by depolarizing and non-depolarizing neuromuscular relaxants. Br J Anaesth 1990;64:21–7. [article]