Gluteal rhabdomyolysis and renal failure due to simvastatin and amiodarone

A 54-year-old man on anticoagulation therapy with phenprocoumon was referred for suspicion of spontaneous gluteus muscle hematoma under therapy with phenprocoumon. He had woken up the day before with debilitating pain in the gluteal region and was not able to rise from his bed. The patient was fully conscious and could not recall any recent trauma; however, he mentioned that the day before the pain occurred, he made telephone calls in a sitting position for 2 hours to make funeral arrangements for his mother. The patient’s medical history was remarkable for cardiac surgery 4 years previously with coronary artery bypass grafting and aortic valve replacement, and for atrial fibrillation. Clinical examination revealed tender and tense swelling of his buttocks. Intravenous contrast computed tomography scans (Figure 1) and a lumbar magnetic resonance imaging scan revealed edematous swellings of the gluteus maximus but ruled out hematoma. The patient was anuric with a plasma creatinine of 344 μmol/l and a creatine kinase of 57,270 U/l. A circumscribed gluteal rhabdomyolysis with acute renal failure was diagnosed. Assessment of the myotoxicity of the patient's medication revealed that amiodarone was added to the previously well-tolerated long-term therapy with simvastatin 4 months before hospitalization. Both medications were discontinued, and, with alkaline diuresis, urine output increased to > 400 ml/2 hours, and within 4 days plasma creatinine improved to 90 μmol/l and creatine kinase to 5968 U/l. An increased risk of rhabdomyolysis with simvastatin and concomitant use of CYP3A4 inhibitors such as amiodarone is described in the literature. However, the isolated occurrence of gluteal rhabdomyolysis in this patient is a rare condition and may have been triggered by prolonged sitting.