Atraumatic trismus induced by duloxetine: an uncommon presentation of acute dystonia

Abstract

Atraumatic trismus can be one of the presentations of medication-induced acute dystonia, particularly by antipsychotics and less commonly antidepressants. A case of an unusual emergency presentation of atraumatic trismus on initiation of duloxetine is reported. The patient was a 40-year-old woman experiencing sudden difficulty in mouth opening and speaking due to a stiffened jaw after taking 5 days of duloxetine prescribed for her fibromyalgia-related chest pain. Assessment of vital signs is prudent to ensure there is no laryngeal involvement. Other physical examinations and her recent investigations were unremarkable. She was treated for acute dystonia and intravenous procyclidine was given together with oral diazepam. Her symptoms improved immediately and her duloxetine was suggested to be stopped. To our knowledge, this is the first case of isolated trismus induced by duloxetine. Clinicians should be aware of this risk, especially considering the limitation of important physiological functions (such as swallowing, eating, etc) associated with this condition.

Background

Trismus commonly refers to the restriction of the range of motion of the jaws caused by a prolonged spasm of the muscles of mastication. Trismus, or locked jaw, has a long list of aetiologies with trauma on top of the list of differential diagnoses.¹ With regards to the atraumatic trismus, medication-induced acute dystonia is one of the important considerations. Psychotropic medications have long been associated with acute dystonia, particularly antipsychotics via its dopaminergic antagonistic property and less commonly antidepressants.² Duloxetine is an antidepressant medicine, known as a serotonin and norepinephrine reuptake inhibitor (SNRI) which is used for depression and anxiety. Little is still known regarding the association between SNRI and acute dystonia. A case of an unusual and peculiar extrapyramidal reaction of atraumatic trismus associated with administration of duloxetine is reported here.

Case presentation

A 40-year-old woman presented to the emergency department (ED) with a sudden onset of difficulty in opening her mouth, speaking and chewing food due to a stiffened jaw. This presentation was her first experience and there was no history of recent trauma. The only noticeable change was the recent initiation of duloxetine 20 mg twice a day for the past 5 days aiming to treat her fibromyalgia-related chest pain. She did not experience abnormal movement or stiffness over other body parts, respiratory distress or hoarseness of voice. There was no feature suspicious of serotonin syndrome or infection, including fever or excessive sweating. The diagnosis of fibromyalgia was made after her regular visits to the ED and general practitioner (GP) for chronic intermittent chest pain which was associated with other non-specific body aches. She was initially treated with short-term paracetamol and non-steroidal anti-inflammatory drugs although the improvement was minimal. Her psychiatric history was negative. She has background history of asthma and hypersensitivity pneumonitis. Her regular medication includes salbutamol inhaler two puffs when necessary, montelukast 10 mg once a day and prednisolone 20 mg once a day. The physical examination revealed an anxious woman with a locked jaw and aphasia. There was no respiratory distress and her vital signs were within the normal range. Other examinations, including neurological, were unremarkable. Given her recent investigations were normal, the diagnosis of acute dystonia was made and intravenous procyclidine 5 mg was given together with oral diazepam 5 mg.

Outcome and follow-up

Her trismus resolved immediately and she was able to move her jaw and speak normally before her discharge from the ED with procyclidine for another 3 days and suggestion to discontinue her duloxetine and follow-up in her GP. Complete remission of symptoms occurs by 2-month of follow-up once duloxetine was discontinued.

Discussion

Duloxetine acts mainly through the inhibition of the reuptake of both serotonin and norepinephrine, and to a lesser extent on dopamine. Other than its mental health indications for the major depressive disorder and generalised anxiety disorder, duloxetine is found to be helpful for neuropathic pain and stress incontinence.³ The prescription in this patient is meant to improve her fibromyalgia-related pain. The main side effects of duloxetine are gastrointestinal-related, including nausea, vomiting, appetite change, weight gain, constipation and dry mouth, on top of uncommon sexual dysfunction.⁴ Although it is uncommon, cases of duloxetine-induced extrapyramidal side effects have been reported, that is, dystonia,^5–8 akathisia,⁹ parkinsonism¹⁰ and tardive dyskinesia.^{11 12} There is no report on isolated trismus without the presence of other dystonic or dyskinetic movements, which is experienced by our patient. Characterised by sustained and marked muscle contractions, acute dystonia can happen to different body parts, such as the extremities, face, neck, abdomen, pelvis or larynx. The painful locked jaw is a terrifying experience and the concern is the laryngeal involvement which is life-threatening.¹³ Adverse drug reaction probability scale (Naranjo) is a common method used to assess a causal relationship between an identified drug and the occurrence of an adverse effect by using 10-item questionnaire.¹⁴ According to Naranjo algorithm, our patient scores 5, that is, ‘probable adverse drug reaction’ as follow; ‘Yes’ (+2) applies for ‘Did the adverse event appear after the suspected drug was administered?’ question, ‘yes’ (+1) applies for ‘Did the adverse event improve when the drug was discontinued or a specific antagonist was administered?’ question, ‘no’ (+2) applies for ‘Are there alternative causes that could on their own have caused the reaction?’ question. Although the pathophysiology of acute dystonia is not entirely certain, it is thought to be due to the imbalance dopaminergic neurotransmission as a result from increased serotonergic and noradrenergic action as most of the drug-induced dystonia is related to antipsychotic and antidepressant drugs.¹⁵ The epidemiological data of our patient correlates with Hawthorne, including the development of acute dystonia reaction within the first 7 days of medication use, the age range from 12 to 78 years and a low dose of duloxetine is enough to trigger acute dystonia.¹⁶ It is uncertain whether the duloxetine-induced acute dystonia reaction is dose-dependent at this stage. The treatment of acute dystonia usually involves the use of parenteral anticholinergic and benzodiazepine for symptomatic relief.¹⁷ More importantly, the culprit medication needs to be stopped. To our knowledge, this is the first case of isolated trismus induced by duloxetine. Clinicians should be aware of this risk, especially considering the limitation of important physiological functions (such as swallowing, eating, etc) associated with this condition.

Patient’s perspective.

The immediate relief of my symptoms had reassured that my condition was not immediately life-threatening although it was a distressing and scary experience, given the inability to verbalise the problem as part of the adverse reaction.

Learning points.

• Although it is uncommon, acute dystonia can happen in patients taking antidepressants, including duloxetine.

• Assessment of vital signs is crucial to ensure there is no laryngeal involvement.

• The management of acute dystonia includes the use of anticholinergic medication for symptomatic relief and stopping the triggering medication once it is established.