A case of mirtazapine induced dystonia

Background: Previous reports indicate that mirtazapine overdose is generally associated with mild and predictable clinical effects, including sedation and tachycardia.¹ We report the management of a case of acute upper limb dystonia associated with mirtazapine overdose in a 20 year old man. Case report: The patient had allegedly taken a mixed overdose of 225mg of mirtazapine and unknown quantities of paracetamol, alcohol and veterinary furosemide sometime previously. He initially complained of nausea which settled spontaneously and initial examination was unremarkable apart from alcohol intoxication. Plasma paracetamol was undetectable and coagulation, renal and liver function test results were within normal limits. Approximately 14 hours following presentation, the patient complained of a painful spasm of both his hands which began very suddenly. Tone was increased in all hand muscles. Neurological examination was otherwise unremarkable. His temperature was 37.7^oC but physical examination did not reveal any other abnormalities. Plasma calcium concentration adjusted for albumin concentration was within normal limits (2.34mmol/L). Arterial blood pH was 7.47, while the base excess was 3mmol/L and oxygen and carbon dioxide tensions were within normal limits. A slow intravenous bolus of calcium gluconate had no effect on the spasm. Procyclidine was given as an intravenous bolus of 10mg and the patient described a reduction in the pain in his hands within 15 minutes of treatment, although it took 4 hours for the spasm to resolve completely. Serum mirtazapine and nor-mirtazapine concentrations 15 hours post-presentation were 115ug/L (normal 20–100) and 97ug/L respectively. His creatine kinase was raised at 639U/L, settling to 281U/L the next day. References: 1. Waring WS, Good AM and Bateman DN. Lack of significant toxicity after mirtazapine overdose: A five-year review of cases admitted to a regional toxicology unit. Clin Tox 2007; 45:45–50