Dramatic response of dropped head sign to treatment with steroid in Parkinson's disease: report of three cases.

Neck dystonia is the most common cause of dropped head sign in parkinsonism. Isolated neck extensor myopathy, which is a rare condition, can also cause dropped head sign in parkinsonism, but no improvement has been achieved with immunosuppressive therapy. We report three cases of treatable neck extensor myopathy causing dropped head sign in patients with Parkinson's disease. Needle electromyography and magnetic resonance imaging suggested a restrictive active myopathy affecting neck extensor muscles. All cases responded dramatically to steroid therapy. Routine needle electromyography should be performed to explore treatable myopathy in Parkinson's disease.