We report the case of a 28-year-old female out-patient with bipolar disorder, whose symptomatology was well-controlled with lithium carbonate 1200mg (orally) (0.9 mEq/l plasma levels) and risperidone 1-2 mg (orally) daily. The patient had been treated for several years in our department and the course of her illness was well-known; it showed that only lithium was both effective and well-tolerated (topiramate was not effective and carbamazepine caused a rash) and only in coadministration with low doses of risperidone.

However, the use of risperidone caused a large increase in prolactin levels (above 2000 μU/l, with normal values below 500 μU/l) and amenorrhoea (the rest of the hormonal investigation and brain magnetic resonance imaging were normal). The patient was put on 5 mg olanzapine (orally), but she did not tolerate this agent because it made her feel ‘confused’ and ‘tired’. She was then put on 200 mg quetiapine (orally). Within 24 h the patient manifested diffuse muscle pains and headache. She reported that her legs were stiff and she had pain in her knee joints. Neurological examination was normal, as were blood and biochemical tests including creatine phosphokinase. Vital signs were normal. No extrapyramidal signs or symptoms (especially akathisia) were present. The pain persisted for 5 more days and the patient demanded that quetiapine be discontinued. The pain disappeared within the first 48 h of shifting back to risperidone, which was according to the wishes of the patient. Six months passed and the patient is still free from symptoms.

To our knowledge, this is the first report of this kind of adverse effect related to quetiapine. Various other antipsychotics, including haloperidol and olanzapine, are reported to cause muscle pain and rigidity because of rhabdomyolysis, but the current case had no laboratory or clinical findings related to rhabdomyolysis.