Treatable lower motor neuron disease due to vitamin D deficiency and secondary hyperparathyroidism.

Vitamin D deficiency and osteomalacia are frequently associated with muscle weakness and atrophy. We present a 78-year-old man with complaints of progressive painless weakness who was referred to us with a diagnosis of suspected motor neuron disease. Results of the neurological examination were remarkable, showing diffuse limb weakness and atrophy, rare fasciculations, normal sensory examination, no bulbar weakness, and no upper motor neuron signs. Electromyography revealed mild chronic changes, denervation and re-innervation, without fibrillations or positive waves. Serum laboratory studies showed an elevated serum parathyroid hormone and markedly reduced vitamin D level. Although the etiology of the vitamin D deficiency was not determined, the patient made a substantial clinical improvement following vitamin D therapy. Vitamin D deficiency and secondary hyperparathyroidism need to be included in the differential diagnosis of patients presenting with a progressive lower motor neuron disease.