Trismus… gnashing of the teeth

Authors: Autumn Kresha, MD, Angelina Vishnyakova, MD, Kurt Lucas, MD (@KurteL10), Hilary Fairbrother, MD, MPH (@hilaryfair) // Edited by: Alex Koyfman, MD (@EMHighAK) and Brit Long, MD (@long_brit)

First, a case…

A 42-year-old male with a PMH of obesity, DM, and HTN presents to the ED with facial swelling and pain. According to the patient, his symptoms all started with dental pain in his left posterior molar about 7 days ago. He has noticed progressively worsening pain and swelling throughout the week.

He went to his dentist two days ago, and the dentist drained an abscess and started the patient on PO amoxicillin. Despite the procedure and taking his antibiotics as directed, the patient states that his symptoms continue to worsen, and today he developed erythema over his left face and chin, a hoarse voice, difficulty swallowing, and fevers to 101 F.

On initial assessment, you notice significant left facial swelling reaching down to the chin and left anterolateral neck, along with erythema to the face and neck. The patient seems to be managing his secretions, but he does have a muffled voice. Upon examination, you notice fullness underneath the patient’s tongue, the patient is only able to open his mouth approximately 2 finger widths, and the patient is unable to flex or extend his neck without significant discomfort. The patient is unable to lay flat or he begins to cough and choke on his secretions. His position of choice is sitting upright with his head and neck directly erect. You hear no stridor, the patient’s pulse oximetry is 99% on RA, and his lungs are clear to auscultation bilaterally.

What should be on your differential for this patient? If his airway became compromised, what airway techniques should you consider?

By description, this patient has trismus, the initial cause likely stemming from a dental infection which is now causing an infection of the deeper spaces below the tongue and jaw.  In other words, this patient appears to have Ludwig’s angina.

This post will look at trismus, but first, how is trismus defined?

Trismus is derived from the Greek word, trismus, or “gnashing (of teeth).”i Traditionally, it was used to describe the spasm of muscles of mastication, but it is now more loosely used to refer to the inability to open one’s mouth fully from any etiology.ii  There is some variation on the exact measurement of the functional cut-off for trismus, however, 35 mm is often used.iii In clinical practice, it’s a spectrum that vary widely based on the patient’s size, age, and baseline. If unable to open 3 finger widths, oral intubation will likely be difficult.iv

Anatomy and Pathophysiology

The temporalis, masseter and medial pterygoid muscles are responsible for jaw closure at temporal mandibular joint. These closure muscles are much stronger than their opening counterparts, which makes overcoming spasmodic trismus impossible. While the inciting source of trismus might be unilateral, the effect is often bilateral due to increased tone mediated by the efferent portion of the reflex arch of the trigeminal nerve.ii


Prevalence varies widely, partially due to the aforementioned lack of standard definition. In addition, there is a vast range of pathologies that cause trismus. While a fairly common finding in patients with head/neck radiation treatment, it is very rare in common diseases such as pharyngitis.ii


Differential diagnosisi-iv


  • Acute tetanus (caused by tetanospasmin toxin made by clostridium tetani, evidence of wounds, history of no vaccination)
  • Retropharyngeal abscess (sore throat, fever, torticollis)
  • Ludwig’s angina (neck and mouth floor edema)
  • Peritonsillar abscess or tonsillitis (fever, sore throat, muffled voice, uvula deviation)
  • Suppurative parotitis (fever, parotid tender, Stensen’s duct drainage)
  • Masticator space infections (fever, masticator tenderness/edema)
  • Malignant otitis externa (diabetics/immunosuppressed)
  • Dental abscess (3rd molar or “wisdom tooth” infection most commonly)
  • Osteomyelitis of the jaw (fever, dental carries, dental/jaw pain)
  • Meningitis (fever, headache, neck stiffness, AMS)
  • Cerebral abscess (fever, AMS, headache)
  • Rabies (late finding, exposure, strange behavior, hypersalivation, AMS)


  • Dystonic reaction (history of recent new drug or increase in dose)
  • Malignant hyperthermia (most often occurs with anesthesia)
  • Strychnine poisoning
  • Black widow spider envenomation (α-latrotoxin)
  • Alcohol withdrawal/DTs (tachycardia, tremulousness, seizures)
  • Commonly used ED drugs known to cause trismus include succinylcholine (drug induced masseter spasm), compazine and metoclopramide (extrapyramidal effect), also can be seen with tricyclic antidepressants


  • Zygomatic arch fracture (can affect coronoid process and inhibit mouth opening)
  • Mandible fractures (can be secondary to the fracture or caused by comminuted bone fragment in the TMJ)
  • TMJ dislocation

 Head and neck tumors/oral cancer

Temporomandibular joint dysfunction

  • Trigeminal neuralgia (severe intermittent unilateral pain of trigeminal nerve)
  • TMJ arthritis/synovitis/disk displacement (pain with palpation lateral to the joint capsule, clicking of joint)


  • Dental nerve blocks (can last 2-5 days after inferior alveolar nerve block secondary to improper technique and formation of a hematoma/fibrosis, hot packs and stretching are used to treat if this is the cause although an infected hematoma may become a surgical emergency)
  • Radiation induced trismus
  • Surgical extraction of mandibular molars
  • Wired jaw (after facial fractures)


  • Hysterical trismus/conversion disorder


  • Trismus pseudo-camptodactyly syndrome (rare congenital condition)
  • Lupus
  • Scleroderma
  • Hypocalcemia (history of recent thyroid/parathyroid surgery, renal failure)
  • Status epilepticus
  • Stiff man syndrome, Lambert-Eaton syndrome (rare neurologic disorder, often paraneoplastic from antibodies to the calcium channels in the body, usually involves muscles of trunk, treated with benzos)ix


There is a very broad differential for trismus. A thorough history will allow you to narrow the cause to one of the aforementioned categories, if not to a particular diagnosis. The diagnosis of trismus is clinical. Always evaluate for facial symmetry. Unilateral swelling should raise your suspicion for infectious or traumatic causes. Palpate the facial/neck musculature, soft tissue, and sublingual area. Always assess the sublingual area in a patient with a history concerning for an intraoral infection. You do not want to miss an early Ludwig’s Angina. While your dental consult might request it, there is limited utility of a panoramic x-ray in the emergency department if there is no reported history of trauma. Consider CT face and/or soft tissue neck with IV contrast when assessing for infectious sources. A CT facial bones without contrast for traumatic causes is recommended. A quantifiable measurement of trismus is useful in order to track progression/improvement and relay these findings to consultants. A maximum oral opening measurement should be obtained.


Treat underlying cause, if possible. For example, if the etiology is infections then typically early steroid administration and antibiotics are appropriate. Pain management may assist mouth opening when there is a traumatic cause. Though rare, dystonic reactions can progress to trismus and even airway compromise. The management is intravenous diphenhydramine. Malignant hyperthermia with masseter muscle rigidity can result from the commonly used intubation drug, succinylcholine. Dantrolene is used in these cases. Benzodiazepines would be the management for seizures and alcohol withdrawal causes. Ultimately, patients with trismus may require paralysis and intubation as the patient’s airway status necessitates.

Airway Considerationsiii,vii,viii

Traditional direct or video assisted oral intubation will likely be very difficult. Depending on the trismus severity, it might be impossible to introduce airway devices into the oral cavity. Even successfully overcoming this obstacle may present the intubator without a sufficient view. Fiberoptic intubation is an important tool for this scenario. Hopefully, the underlying etiology of the trismus does not extend into the nasopharyngeal space allowing a fiberoptic nasal intubation to bypass the issue. An awake intubation is ideal. Depending on resources, other techniques including blind nasal intubation or video assisted/bougie may be helpful. If all else fails, or the patient is deteriorating too rapidly to attempt other techniques, the surgical airway should be considered. If possible, consider another paralytic aside from succinylcholine. Succinylcholine has a known adverse reaction of inducing masseter spasm.

  • Traditional direct or video assisted oral intubation will likely be difficult!
  • Fiberoptic nasal intubation is the best option!
  • Use awake intubation if at all possible
  • Other options include blind nasal intubation or video assisted/bougie.
  • If all else fails, move to surgical airway
  • Avoid succinylcholine if possible, as this may cause further spasm

Back to the case…

Because of his significant facial/neck edema, positional airway, changes in voice, trismus, dysphagia, and neck immobility, there is a high concern for airway deterioration. This patient’s constellation of signs/symptoms should trigger one to think that this will be a difficult airway to obtain by typical RSI/orotracheal intubation strategies and an awake naso-tracheal intubation was considered. The patient was prepared with nebulized and/or atomized lidocaine along with viscous lidocaine on a nasal trumpet to coat the nasal passages. Using midazolam/ketamine for sedation, the patient was nasally fiberoptically intubated with a 6.0 ETT. The patient was treated with IV ampicillin/sulbactam, IVF 30 cc/kg normal saline, and the patient was taken to the OR to have the abscess causing his Ludwig’s angina drained. A day later the patient was extubated and he was discharged the following day.

Key Points

  • Trismus is masseter muscle spasm causing an inability to open the mouth.
  • The differential diagnosis is wide including infection, medication, trauma, head & neck cancer, iatrogenic…
  • Treat the underlying cause of the trismus.
  • Airway protection may be needed – think fiberoptic nasal intubation, awake intubation, or video assisted intubation.
  • Avoid succinylcholine.
  • Have a surgical airway prepared as plan B.


Resources/Further Reading

[i]Trismus. Merriam-Webster, Incorporated, 2019. Retrieved from

[ii]Santiago-Rosado LM, Lewison CS. Trismus. [Updated 2019 Apr 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan. Available from:

[iii]Dijkstra, Pieter & Huisman, P.M. & Roodenburg, Jan L N. (2006). “Criteria for trismus in head and neck oncology”. International journal of oral and maxillofacial surgery. 35. 337-42. 10.1016/j.ijom.2005.08.001.

[iv]Vissers RJ, Danzl DF, Serrano K. Intubation and Mechanical Ventilation. In: Tintinalli JE, Stapczynski J, Ma O, Yealy DM, Meckler GD, Cline DM. eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8e New York, NY: McGraw-Hill; 2016. Accessed May 29, 2019.

[v]Sertraline-Induced Rhabdomyolysis, Trismus, and Cardiac Arrest in a Child. Peter J. Holmberg, Grace Arteaga, Brenda M. Schiltz, James Homme Pediatrics Oct 2018, 142 (4) e20180804; DOI: 10.1542/peds.2018-0804

[vi]Preventing Trismus. Memorial Sloan Kettering Cancer Center. Published December 7, 2015. Accessed June 8, 2019.

[vii]Fernández-Frackelton, Madonna. Rosen’s Emergency Medicine: Concepts and Clinical Practice: 9th edition, Chapter 121, 1573-1597. Elsevier, Inc 2018. Accessed 21 Oct 2017.

[viii]Dhanrajani, PJ, Jonaidel, O. “Trismus: aetiology, differential diagnosis and treatment.” Dent Update. 2002 Mar;29(2):88-92, 94.

[ix]Chapter 31. Intracranial Neoplasms and Paraneoplastic Disorders. In: Ropper AH, Samuels MA, Klein JP. eds. Adams & Victor’s Principles of Neurology, 10e New York, NY: McGraw-Hill;2014. Accessed June 06, 2019.


One thought on “Trismus… gnashing of the teeth”

Leave a Reply

Your email address will not be published. Required fields are marked *