A rare neurological disorder comprising fluctuating trunk and limb stiffness, painful muscle spasms, task-specific phobia, an exaggerated startle response, and ankylosing deformities such as fixed lumbar hyperlordosis. Age of onset peaks around 45 and symptoms develop over months or years. Progressive muscle stiffness renders the trunk and hips immobile and the gait becomes stiff and awkward. The presence of antibodies against glutamic acid decarboxylase (GAD-Abs) in more than 70% of cases suggests an autoimmune pathogenesis. GAD-Abs may block synthesis of the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA) thereby attenuating inhibition of spinal motoneurones.