Brachial monomelic amyotrophy as an initial manifestation of stiff person syndrome

Stiff person syndrome (SPS) is characterized by rigidity of truncal and proximal muscles. The presence of abdominal and paraspinal rigidity is a defining clinical feature of SPS. It is rarely associated with the lower motor neuron (LMN) features. We report a patient with SPS whose initial clinical presentation was that of brachial monomelic amyotrophy (BMA). A 24-year-old gentleman presented with a history of the left upper limb wasting and weakness. In addition, he reported stiffness of the lower limbs and abdomen while walking. On examination, patient had left upper limb monomelic amyotrophy and hypertonia, exaggerated deep tendon reflexes in all four limbs. He also had abdominal and paraspinal rigidity. Serum was strongly positive for GAD 65 antibodies suggestive of SPS. Patient showed dramatic improvement to immunomodulation. Patient presented with features of BMA. Symptoms related to SPS were mild. Abdominal rigidity was the clue to the diagnosis. LMN features have been reported previously in stiff person plus syndrome with an atypical course and progressive encephalomyelitis with myoclonus and rigidity, but not in classical SPS.