Atomoxetine-related bruxism in a 7-year-old boy: A case report

Sir,

Atomoxetine is a selective noradrenaline reuptake inhibitor (SNRI), and the United States Food and Drug Administration approved in 2002 for the treatment of attention deficit hyperactivity disorder (ADHD).[1] The most common side effects of atomoxetine are headache, abdominal pain, decreased appetite, vomiting, somnolence, and nausea.[2] Three cases with aggravating bruxism caused by atomoxetine were reported in the literature.[3,4,5] Bruxism has not been defined before or after marketing of atomoxetine.[6] As we know, this is the fourth reported case of bruxism due to atomoxetine use.

A 7-year-old boy was referred to our outpatient clinic with complaints of talking too much, running, or climbing excessively when it is inappropriate, difficulty in paying attention to details and finishing schoolwork, easily distracted, making careless mistakes at school, and shifting from one uncompleted activity to another, excessively for about 2 years. Kiddie Schedule for Affective Disorders and Schizophrenia for School Age Children- Present and Lifetime Version (K-SADS-PL)[7] was conducted. The case was diagnosed with ADHD according to the DSM-5 criteria.[8] Atomoxetine 10 mg/day was prescribed. After 7 days of medication, the parents noticed that the child was grinding his teeth every night. Bruxism was sufficiently loud to be heard from other rooms. In subsequent days, the patient began to complain of jaw pain, which lasted all day. The patient's parents presumed that this can be a side effect of atomoxetine and then visited our outpatient clinic. Because the drug-related event was suspected, atomoxetine was discontinued. Following the discontinuation of atomoxetine, bruxism ceased. After 2 weeks, because of having ADHD symptoms, atomoxetine was restarted at the dose of 10 mg/day and then bruxism reappeared. The probability of an adverse drug reaction was assessed with the Naranjo probability scale,[9] and the score was 8, which indicated a probable association between atomoxetine. We decided to start methylphenidate. Methylphenidate 10 mg/day was prescribed. After 7 days of medication, methylphenidate dosage was increased to 20 mg/day. In the 4^th week, the patient's parents and teachers reported significant improvement of attention deficit symptoms and school-related problems. When interviewed, the family did not mention any side effects. Bruxism was not observed during follow-up of 3 months.

Psychostimulant drugs and atomoxetine are a choice of the treatment for children with ADHD. There is often an immediate and dramatic improvement in the academic performance of children with behavioral disturbances after administration of the medication. Although there are studies in the literature indicating the association of ADHD symptoms (especially hyperactivity) with bruxism,[10,11] bruxism in our case occurred after the initiation of atomoxetine. Bruxism continued during atomoxetine treatment and was completely eliminated after discontinuation. The patient had no symptoms of bruxism before using atomoxetine. Therefore, it was thought that the bruxism diagnosed at the patient may be related to atomoxetine, rather than ADHD itself. Although there have been lots of publications about the improvement of bruxism with methylphenidate medication, at present, it is little understood and the literature is controversial regarding the mechanism for bruxism.[12] However, recent pharmacologic evidence suggests that the imbalance between dopaminergic and serotoninergic system may be involved in the pathophysiology of bruxism, and dopaminergic, serotonergic, and adrenergic systems suppress or exacerbate bruxism activity.[12,13] Atomoxetine is a SNRI. The mechanism for SNRI-induced bruxism may be due to disrupted serotonergic modulation of dopaminergic neurons in the mesocortical tract, which plays a role of controlling musculator motor activity. The complete remission of bruxism was noticed, but ADHD symptoms of the case were increased when atomoxetine was discontinued. However, bruxism was not observed during follow-up of 3 months with methylphenidate treatment.

There are three more cases with aggravating bruxism caused by atomoxetine in the literature.[3,4,5] To our knowledge, this is the fourth reported case of bruxism related to atomoxetine. We conclude that there was a probable relationship between atomoxetine and bruxism based on our observations that bruxism reappeared with the resumption of atomoxetine. Further studies are needed to determine the exact mechanism of this side effect with therapeutic doses of atomoxetine.

CONCLUSION

We should know that atomoxetine causes bruxism when prescribing this drug. And also, the presence of bruxism should be questioned during psychiatric visits after we start atomoxetine.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) and patient's parents has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patient and patient's parents understand that their names and initials will not be published, and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.