What's Up Doc? Stiff person syndrome causes muscles to spasm and/or become rigid

Q: What is stiff person syndrome with which Celine Dion was diagnosed?

A: Stiff-person syndrome (SPS) is a rare neurological disease affecting about 1or 2 out of a million people that may cause the muscles to painfully spasm and/or become stiff/rigid. SPS affects women twice as frequently as men, is more common in people with other autoimmune disorders (such as Type 1 diabetes, thyroiditis, vitiligo, pernicious anemia and others) and usually starts to manifest when the patient is in their 30s to 50s.

There is a lot that is not understood about this rare disorder, but it is believed to have an autoimmune component — part of its cause is the body’s immune system inappropriately attacking parts of the patient’s own body.

Supporting this hypothesis is that most patients with SPS have elevated levels of glutamic acid decarboxylase (GAD) antibodies and/or certain other antibodies. GAD converts glutamate to gamma-aminobutyric acid (GABA), an amino acid necessary for the signals from nerves to muscles to be able to be turned "off."

One way to think about SPS is that it is an autoimmune condition with similarities to tetanus. Tetanus is a disease caused by a neurotoxin produced by the bacterium Clostridium tetani. This toxin inhibits the release of GABA and glycine and by doing so blocks the nerves "off" signal, effectively locking the nerve into the "on" position and causing "lockjaw" and/or other muscle rigidity.

SPS is categorized in one of the following ways:

• Classic SPS. This is the most common variant (up to 80% of SPS patients). Symptoms typically start in the "core" muscles of the trunk (including the chest), abdomen, back and/or proximal limbs. As Classic SPS progresses, it may involve the more distal aspects of the arms, legs and other muscle groups. Symptoms of SPS insidiously fluctuate at its onset, but may then worsen over time. This is one reason it may take five years or longer for a diagnosis to be made. For some patients the muscle spasms may eventually become so severe as to dislocate joints and even break bones.

• Partial SPS. The 10% to 15% of SPS patients with this condition have specific parts of their body affected, most commonly one leg. Especially when the involvement is asymmetric, it can cause problems with coordinated movements.

• Other uncommon forms of SPS.

SPS patients may have increased sensitivity to noise, touch and/or emotional situations that may trigger their symptoms. As symptoms progress (usually over five to 20 years or more) patients may develop a hunched-over posture, eventually becoming unable to walk and/or losing the functional use of the muscle groups affected.

SPS is diagnosed based on the symptoms, history and physical examination, and is corroborated by ruling out other conditions that may affect the muscles (such as Parkinson’s disease, multiple sclerosis, etc.) and measuring antibody levels to GAD and/or other antibody levels. Other tests to evaluate muscle function, such as an EMG (electromyography), may be indicated.

To date there is no specific treatment for SPS. Instead, treatments are focused on mitigating spasm/rigidity symptoms (for example, using muscle relaxants and/or other medications) and using general immunotherapeutic approaches to "calm" the patient’s immune system (for example, using intravenous immunoglobin treatments, plasmapheresis and/or certain other treatments).

Anyone having muscle spasms, muscle rigidity or other concerning symptoms should speak with their health care provider. The insidious onset and rarity of SPS makes it difficult to diagnose, especially since the initial symptoms may be subtle and physical exam findings, especially early in the course of the disease, may be minimal or absent. Hence an awareness of this condition and vigilance to follow suspected symptoms is key to figure out what is going on. If SPS is suspected, the patient should be referred to a specialist with experience and expertise diagnosing and treating this rare disorder.

Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com

This article originally appeared on MetroWest Daily News: Dr. Jeff Hersh discusses symptoms of stiff person syndrome