Introduction

Stiff-person syndrome (SPS), formerly termed stiff-man syndrome and Moersch–Woltmann syndrome, was first described in 1956 as a condition of muscular rigidity and episodic spasms that principally involved the trunk and lower limbs (Moersch & Woltman, 1956). The idiopathic (typical) form of SPS is now considered an autoimmune disorder, often associated with type I diabetes and increased levels of antibodies against glutamic acid decarboxylase (GAD), the enzyme that catalyzes gamma-amino butyric acid from glutamic acid. Symptoms usually begin during adult life and affect both sexes. Early in the disease course symptoms can be confused with orthopedic conditions, but as the disease progresses, a clear distinction can be made. Increasing symptoms of axial and limb rigidity and painful muscle spasms eventually lead to disability. Electromyography demonstrates continuous and spontaneous firing of motor units in the rigid muscles.

Clinical features

Brown and Marsden (1999) describe a typical form (classic) and several atypical forms (i.e., plus variants) of SPS. The typical form of SPS is characterized by progressive axial rigidity predominantly involving the paraspinal and abdominal muscles along with hyperlordosis of the lumbar spine, and spontaneous or stimulus sensitive disabling muscle spasms of the abdominal wall, lower extremities, and other proximal muscles. Muscle rigidity in typical SPS is attributed to dysfunction of the inhibitory interneurons of the spinal cord. These patients have high incidence of anti-GAD and islet cell antibodies (ICA) (96% GAD-65 antibodies and 89% ICA in Mayo clinic series) (Walikonis & Lennon, 1998).