Stiff Person Syndrome

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69 Stiff Person Syndrome

This chapter concentrates on the most common of the very uncommon motor neuron hyperactivity disorders, namely the stiff person syndrome. Two other potentially related syndromes characterized by incomplete relaxation or inhibition of motor neurons—Isaac (Merten) syndrome and neuromyotonia—are discussed in Chapter 70.

Clinical Vignette

A 53-year-old woman with myeloid metaplasia reported a 6-month history of severe back pain, difficulty walking, and occasional falls. No lumbosacral disc disorder could be identified. During the past month, these spasmodic muscle pains of her legs, back, and abdomen were induced by attempting to sit up, stand, or walk. Occasionally, these spasms led to stiffening of her entire body; at their extreme these induced urinary incontinence. At times, the severity of the pain led her to cry out to such a degree that it caused one observer to liken her distress to that of a “bellowing cow”! These outbursts led to her being referred to a psychiatrist.

Neurologic examination demonstrated an anxious and alert middle-aged woman. The primary finding was her spontaneous reaction to the slightest sensory stimuli wherein she totally stiffened, reminding this neurologist (HRJ) of a tetanus patient. Other than hyperlordosis, marked hyperreflexia at her knees and a right Babinski sign, her basic neurologic examination was normal. However, on a neurosurgeon’s brusque attempt to get her out of bed to stand, she developed severe painful body spasm and fell into the hospital room wall as if a chain saw had cut her legs off.

Head and cervicothoracic spine magnetic resonance imaging (MRI) and cerebrospinal fluid (CSF) study were normal, as was serum B12 level. Nerve conduction studies were normal. Her needle electromyography (EMG) study demonstrated prolonged motor unit activity in contracting muscles during episodes of stiffness and spasm but was otherwise normal. Double-antibody radioimmunoassay demonstrated a high level of serum glutamic acid decarboxylase 65 (GAD-65) antibodies (138 nmol/L; reference range: ≤0.02 nmol/L). The patient was diagnosed with stiff person syndrome (SPS).

Increasing doses of diazepam alleviated symptoms at a dose of 60 mg daily. A course of plasmapheresis treatments followed by prednisone (80 mg daily) led to gradual symptomatic improvement. She was successfully tapered off corticosteroids during a 2-year period and diazepam over 5 years.

The stiff person syndrome (SPS, originally known as the stiff man syndrome) was first described by Moersch and Woltman in 1956. Classic stiff person syndrome is a chronic autoimmune disease characterized by spine and leg rigidity with lumbar hyperlordosis and painful spasms. Women are more often affected than men at a ratio of 2 : 1. This disorder generally presents in the fourth through sixth decades. Its onset is typically insidious and the course is usually progressive.

Laboratory studies that are classically abnormal in SPS include an elevated serum GAD-65 antibody titers (>20 nmol/L), needle EMG findings of continuous motor unit activity in at least one axial muscle, and normal brain MRI and CSF studies. Variants of SPS include those with focal limb dysfunction (stiff limb syndrome), encephalomyelitis (“SPS Plus”), and those associated with paraneoplastic antibodies, namely, amphiphysin as seen with breast cancer. Although most instances of SPS do not have a family history, at least one instance of such is reported. Interestingly the parent and propositus had a stiff limb variant and the daughter a purely intermittent axial presentation initially diagnosed as hysteria or anxiety disorder because of her presentation with recurrent opisthotonus.