Olanzapine is a new atypical antipsychotic drug with proven efficacy in several psychiatric conditions such as schizophrenia and autism. In a pharmacovigilance study of Olanzapine in 8858 patients in the UK, the main adverse effects were: somnolence with sedative effect, extra-pyramidal signs, weight gain, lassitude, agitation, liver abnormalities…[3]

In a study based on cases reported to the WHO International Drug Monitoring Collaboration, Mannesse and all found that Olanzapine was the second most common atypical antipsychotic associated with hyponatremia/ISADH, after risperidone [4].

In animal models, it has been shown that Dopamine has an inhibitory effect on ADH secretion. This effect can be blocked by dopamine receptor antagonists. Olanzapine is a selective monoaminergic antagonist with a high affinity for dopamine receptors and causes SIADH through its antagonism to them [5,6].

The association between Olanzapine use and rhabdomyolysis and CPK elevation has also been reported in the literature [7–9]. The exact mechanism associating them remains to be elucidated, however some authors suggest the existence of an important role for serotonin (5-HT), as Olanzapine would have a more potent activity than antagonists of the serotonin receptors of Dopamine. 5-HT is believed to be toxic to skeletal muscle, which contains high-affinity receptors in the sarcolemma, and the cell membrane [10,11].

In our patient, the elevation of CPK and LDH associated with the existence of hyperkaliemia made it possible to retain the diagnosis of rhabdomyolysis, the search for myoglobinuria was not performed. The questioning and clinical examination did not reveal any signs of muscle lysis other than toxic, thus allowing Olanzapine to be considered the direct cause.

The chronology of the symptoms that appeared and worsened concomitantly with the untimely intake of Olanzapine, as well as the improvement and correction of the hyponatremia and rhabdomyolysis following the cessation of the said drug and therapeutic measures, without recurrence, support our diagnostic hypothesis.