Stiff person syndrome associated with lower motor neuron disease and infiltration of cytotoxic T cells in the spinal cord

We present a 67-year-old non-diabetic male who presented with muscle cramps, paresis, atrophy and fasciculations in the left leg, followed by rapidly progressive muscle stiffness and superimposed spasms which subsequently also affected the right leg and the trunk. GAD65 autoantibodies were elevated in serum and CSF, compatible with systemic and intrathecal synthesis of oligoclonal and high-avidity autoantibodies, and GAD65 specific T cells were clonally expanded in the CSF. The patient did not respond to GABAergic and immunomodulatory treatment or plasma exchange, and died from respiratory failure after 18 months. Autopsy revealed unilateral axonal swelling, chromatolysis and vacuolisation of anterior horn cells of the lower spinal cord, accompanied by microglia proliferation and discrete infiltration of CD8+ cytotoxic T cells. No CD4+ T helper cells, B cells or complement deposition were detected. To our knowledge, this is the first report of stiff person syndrome with lower motor signs restricted to a lower limb, and also the first attempt to characterize the infiltrating T cells. The finding of CD8+ cytotoxic T cells in the absence of B cells in the inflamed area of the spinal cord suggests that the intrathecal synthesis of GAD65 autoantibodies takes place in areas of the CNS not strictly related to the clinically relevant lesions.