Persistent Camptocormia Associated with Atomoxetine in a Child with Attention-Deficit/Hyperactivity Disorder

To The Editor:

Atomoxetine, a selective norepinephrine reuptake inhibitor, was shown to be effective for the treatment of attention-deficit/hyperactivity disorder (ADHD) in children and adolescents in meta-analysis of nine studies (Cheng et al. 2007). The commonest adverse events reported were gastrointestinal (appetite decrease, abdominal pain, vomiting, dyspepsia) and somnolence. We report the case of a child with ADHD who developed persistent camptocormia while being treated with atomoxetine.

Case Report

A 7-year-old boy presented with a history of excess activity, poor attention at school, and falling academic grades over the past 2 years. His parents were informed by the schoolteacher that he would not stand quietly in the prayer line at the morning assembly, and would climb up the window grills of the classroom and frequently disturb his classmates when a lesson was being taught, causing disruption in the class functioning. His sleep and appetite were normal. There was no history of developmental delay, seizures, autistic features, or major medical illness nor was there any family history of neuropsychiatric problems. On behavioral observation, there was hyperactivity with marked distractibility to external stimuli along with frequent impulsive behavior. He had a score of 19 on the Conner's rating scale. A clinical impression of ADHD was noted, and the boy was prescribed atomoxetine 10 mg/day, in consideration of his weight of 20 kg, in addition to behavioral management.

He came for follow-up 1 month later with his parents, who reported significant improvement (50% as per their observation) in both his hyperactivity and inattention, which they corroborated with the class teacher. His Conner's rating score was now 9. However, they observed that after 3 weeks of initiation of medications, the boy had a peculiar change in his posture characterized by a forward bending of his trunk, as a result of which he was not able to sit properly in his chair or look at the blackboard in the class. On examination, his trunk had a forward bend of 60 degrees from the vertical plane, but the rest of his neurological and general medical examination was normal. Investigations, including hematological and biochemical parameters and electrocardiogram (ECG) were unremarkable, and the CT scan of the brain was normal. He was admitted in the child psychiatry unit and because he was believed to have drug-induced camptocormia, atomoxetine was discontinued, and he was put on diazepam 5 mg orally. One week after admission, his posture began to improve, and his back straightened to 45 degrees after 1 month. He was not rechallenged with atomoxetine, as his parents did not wish to risk an exacerbation of the condition again. On the Naranjo adverse drug reaction scale, a score of 7 was noted, indicating a probable association (Naranjo et al. 1981). Methylphenidate (MPH) 10 mg was added to the regime, to which he gradually showed partial response. He has been on regular follow-up for 2 years, during which his ADHD symptoms remained under control with MPH 20 mg and behavioral techniques, and his trunk had ∼ 15 degrees of bend, with which he could walk and attend his school.

Discussion

In our case, the child developed camptocormia, that is, forward bending, 3 weeks after starting atomoxetine. There were no features suggestive of any neurological disorder. On a PubMed search there was no report of camptocormia or dystonia with atomoxetine monotherapy. There are occasional reports of tics associated with atomoxetine (Ledbetter 2005; Párraga et al. 2007; Sears and Patel 2008). Rarely, dyskinetic movements have been reported with atomoxetine, when used along with other medications, which resolved following medication discontinuation (Bond et al. 2007). There were other signs of norepinephrine toxicity as well. Camptocormia at older ages is associated with neurological disorders such as Parkinson's disease, multisystem atrophy, paraneoplastic disorders, and orthopedic conditions such as disc herniation, spinal trauma, or arthritis (Finsterer and Strobl 2010, 2011). It is also observed rarely in some psychiatric disorders including conversion disorders, and as an adverse reaction to psychotropic medications, mostly antipsychotics (Rajmohan et al. 2004; Finsterer and Strobl 2010, 2011). There is one report of camptocormia in a 21-year-old associated with lumbar disc herniation (Duman et al. 2008), and a 14-year-child developed torticollis and camptocormia following neck trauma (Shuper et al. 2007). In both the cases, there was complete resolution of symptoms following treatment. In our case, camptocormia was persistent at the 2 year follow-up, although there was partial improvement with diazepam.

The mechanism underlying this association is not clear, as atomoxetine is a selective norepinephrine reuptake inhibitor, and it has very minimal affinity for any other neurotransmitter transporter or receptor (Ledbetter 2005). One possibility is that norepinephrine influences the concentration and metabolism of dopamine in some indirect manner; therefore, such modulation may have caused the dystonic reaction (Kobayashi et al. 2010). Therefore, our case illustrates a very rare adverse effect, and to the best of our knowledge, it is the first ever case of dystonia presenting as camptocormia in a child as a result of taking atomoxetine, although the persistence of the symptom, and the lack of rechallenge, makes the association at best probable. Nevertheless, this case highlights the need for child psychiatrists to have a high level of suspicion for such a phenomenon, so as to facilitate early detection and prompt management.