Posted by Jennifer Ding, MSIV Drexel University College of Medicine
What is Stiff Person Syndrome (SPS)?
Stiff Person Syndrome (yes, the official moniker) is a very rare autoimmune disease of the nervous system that affects maybe 1 in 1,000,000 people worldwide. Most patients experience fluctuating, involuntary muscle rigidity in the trunk and limbs, an exaggerated lumbar curve, and a heightened sensitivity to their environment.
Loud or unexpected noise, touch and emotional distress can actually set off muscle spasms or even falls in those afflicted.
Attacks of spasms are usually unpredictable, last for minutes and tend to recur over hours. These spasms can be so intense that they actually can cause.
The rigidity seen in SPS is characterized by a stiffness (hence the name) that begins over several months along the spine and spreads to the legs. In the lucky few, the fluctuating rigidity becomes fixed leading to difficulty walking, bending, and frequent falling.
Who gets SPS?
Moersch and Woltman first described SPS in 1956 based on 14 cases that were observed over 32 years. It was initially called “stiff man syndrome” before the disease was found in females and children as well.
Today, we see that SPS affects twice as many women as men and is frequently associated with other autoimmune diseases, such as Diabetes Mellitus Type 1, thyroiditis and vitiligo. Age of onset varies between 30 to 60 with it occurring most frequently in people in their 40s.
What causes SPS?
Now for the science behind SPS: like any autoimmune disease, the problem is thought to lie with antibodies that attack the body’s own cells or enzymes. Patients with SPS have antibodies against glutamic acid decarboxylase (GAD), an enzyme, that produces gamma-aminobutyric acid (GABA), a chief inhibitory neurotransmitter (a chemical) that plays a crucial role in regulating our central nervous systems. GABA is also directly involved in regulating muscle tone.
The exact details of the way GAD antibodies cause SPS remain unknown. Many people with GAD antibodies don’t develop SPS. But most patients with SPS have a high level of GAD antibodies in their blood as well as antibodies that inhibit GABA-receptor-associated-protein (GABARAP). Therefore, scientists hypothesize that the root cause of the muscle rigidity and spasms seen in SPS lie in a GABA impairment.
Think of it this way: muscles work in pairs. When one contracts, the other relaxes, and vice versa. GABA is key in regulating this relaxation and without it, both muscles end up contracting. When both muscles contract, they lose the ability to work together, leading to a stalemate, or stiffness that we see in patients with SPS.
How is SDS diagnosed?
The level of GAD antibodies can be measured in the blood and cerebrospinal fluid (CSF). As aforementioned, the mere presence of GAD antibodies in the blood does not directly correlate with a diagnosis of SPS. Instead, the higher the level of GAD antibodies in the blood, the more likely SPS is the diagnosis.
Electromyography (EMG) can also be used to demonstrate involuntary neuronal firing in muscles.
How is SPS treated?
While there is no cure for SPS to date, there are treatment options that are aimed at symptom relief. Benzodiazepines, such as Valium (diazapam) or Ativan (lorazepam), that act similarly to GABA are the primary treatment for symptom relief. These drugs have muscle relaxant and anticonvulsant effects. Baclofen, another type of GABA-agonist that is dispensed from an implanted pump, can be used as a muscle relaxant. Neurontin (gabapentin) is a seizure medication that has also been used for symptom relief. However, SPS tends to worsen over time, leading to patients requiring increased dosages of drugs.
Intravenous immunoglobulin (IVIG) that target the antibodies themselves are also used in patients with advanced disease. IVIG has been shown to decrease stiffness and the heightened startle reflex. Steroids, rituximab, and plasma exchange have also been used to target the immune system in SPS patients, but the benefit of these treatments remains unclear.
Additional reading material
Click here for more information on SPS, the most up-to-date research on the neurological disease, and social networking for those interested, afflicted, or who have family members who are afflicted.
Click here for an article about a patient with SPS.
News segment about a young dancer with SPS.