Stiff-Man Syndrome

Posted by Elaine Moore Sep 9, 2006

Stiff-man syndrome (SMS), which is occasionally called stiff-person syndrome, is an autoimmune disorder affecting the central nervous system. Stiff-man syndrome causes a progressive condition of fluctuating muscle rigidity and spasms and primarily affects the spine and lower limbs. Muscle stiffness in SMS is caused by excess muscle tension and pressure and often affects the muscles of the neck, shoulders, trunk, arms and legs. Over time SMS can progress and interfere with the ability to walk. Symptoms of stiff-man syndrome typically emerge in adults between ages 30 and 60 years old, and unlike most autoimmune diseases, men are about 7 times more likely to be affected than women. Similar to other autoimmune diseases, symptoms are often triggered by external stimuli, particularly sudden loud noises, and emotional stress.

Stiff-man syndrome was first described in 1956 by Moersch and Woltman. The 14 patients included in this early report were described as resembling tin soldiers with titanic muscle spasms. Later reports show that the simultaneous contraction of agonist and antagonist muscles causes the restriction in mobility that causes patients to walk or fall like wooden men.

Symptoms of Stiff-Man Syndrome

Symptoms in SMS usually appear insidiously and include muscular tightness, stiffness and rigidity involving the axial muscles of the neck, paraspinal and abdominal muscles and later spreading to affect the proximal limb muscles. Paraspinal rigidity may cause low-back pain and a prominent lordosis. The chest muscles may also be affected and in this case shortness of breath can occur. The cranial muscles may also be affected, causing difficulty in smiling, swallowing and speaking.

Along with the persistent muscle rigidity, patients may have muscle spasms, which are frequently triggered by sudden noises or jarring, passive stretching of muscles, and voluntary movement as well as fear, anxiety and apprehension. These spasms may last for several minutes. About 10 percent of patients with SMS also develop symptoms of epilepsy. Before effective treatments were developed for SMS, patients often became totally bedridden.

Diagnosis of Stiff-Man Syndrome

In 1989 the diagnostic criteria for SMS were proposed. These include:

1) Prodrome or onset characterized by stiffness and rigidity in axial muscles

2) Slow progression of stiffness, resulting in impaired ambulation or walking

3) Fixed deformity of spine, usually a pronounced lordosis or swayback, as the disease progresses

4) Presence of superimposed episodic spasms precipitated by sudden movement, noise, or emotional stimuli

5) Otherwise normal findings on motor and sensory examinations

6) Normal intellect

7) Continuous motor-unit activity on electromyelogram (EMG) abolished or improved by intravenous or oral diazepam (Valium).

Since, with the discovery of the autoimmune nature of SMS, it's been determined that about 60 percent of patients with SMS have autoantibodies that are directed against the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), primarily the glutamic acid decarboxylase (GAD) component (anti-GAD antibodies).

In addition to routine electromyelograms, simultaneous video-electroencephalographic-surface electromyelographic recordings may be used to help confirm the diagnosis. Cerebrospinal fluid examinations usually show a normal cell count and occasionally oligoclonal immunoglobulin G (IgG) bands are present although these bands are not seen in the serum.

Other Autoimmune Diseases and malignancies in SMS

Patients with stiff-man syndrome have an increased incidence of organ-specific autoimmune diseases, particularly insulin-dependent diabetes mellitus (IDDM), and also Graves' disease, hypothyroidism, pernicious anemia, polyendocrine syndrome type I, and vitiligo. The co-existence of other autoimmune diseases as well as the development of epilepsy is only seen in patients with SMS who have antibodies directed against GABA producing neurons, usually anti-GAD antibodies. SMS can also occur as a paraneoplastic syndrome in patients with certain malignancies, including breast cancer, pharyngeal cancer, small cell lung cancer and in association with paraneoplastic limbic encephalitis. SMS may occur before the malignancy becomes apparent.

Treatment

Diazepam, because of its ability to enhance the effect of endogenously released GABA on cell receptors, is the most effective treatment for SMS. Other drugs that can offer benefits include clonazepam (Klonopin), oral and intrathecal baclofen and sodium valproate (Depakene, Depakote). Intravenous immunoglobulins have also been used successfully in SMS.

Resources:

Thomas M, Diagnosis: Stiff-person Syndrome, Summary and Differential Diagnosis, Archive Cases BCM Neurology Department.

Bjork E, Vellosos LA, Kampe O, Karlsson FA, GAD autoantibodies in IDDM, stiff-man syndrome, and autoimmune polyendocrine syndrome type I recognize different epitopes, Diabetes, 1994 Jan; 43(1): 161-165.