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Diagnosing SPS

SPS is a rare, progressive neurological disorder characterized by severe muscle spasms that can break bones, dislocate joints, and result in life-threatening breathing problems. The impact on a patient’s quality of life reaches far beyond the physical — challenging their mental, emotional, and social well-being.

No One Single Test for SPS

A diagnosis of Stiff Person Syndrome (SPS) depends on multiple factors. There is no one single lab test or study that determines the diagnosis. A detailed medical history, physical exam, blood tests, and other lab tests can support the diagnosis. Importantly, these tests and their interpretation should be done by a physician who has expertise in the evaluation of SPS. The history should be consistent with one of the forms of SPS described in Types of SPS, most commonly including muscle stiffness of the legs or trunk, usually worsening over months or years.

Since SPS symptoms may overlap with other disorders, an evaluation for SPS would include multiple other blood tests and possibly a spinal tap to examine cerebral spinal fluid (CSF).

70-80% of People with SPS have GAD Antibodies

One useful blood test can detect the presence of antibodies to glutamic acid decarboxylase (GAD). The antibodies are abnormal, while GAD is a normal enzyme. About 70 – 80% of people with SPS have antibodies against GAD.

The absence of GAD antibodies does not rule out SPS.

The presence of extremely high levels of GAD antibodies

strongly supports the diagnosis of SPS in the context of the appropriate medical history and physical exam findings. GAD antibodies may also be measured in the cerebrospinal fluid obtained by a spinal tap. However, GAD antibodies can also be found in other autoimmune neurological disorders and in other autoimmune disorders that are not neurologic, including type 1 diabetes mellitus, thyroiditis, pernicious anemia, celiac disease, and very rarely in certain cancers.

It is worth emphasizing that elevated GAD antibodies do not by themselves determine a diagnosis of SPS. The medical history, exam, and lab findings must also be consistent. Extremely high levels of GAD antibodies are most suggestive of an SPS diagnosis. This highlights the importance of being evaluated by an appropriate medical expert who has the experience to correctly assess these different factors.

Other Antibodies Could Indicate SPS

Glycine receptor antibodies are the second most common SPS antibodies, found in about 10% of SPS patients, followed by amphiphysin antibodies and DPPX (dipeptidyl peptidase-like protein 6) antibodies.

Some neurologists also recommend an electromyogram (EMG), which records electrical activity in affected skeletal muscles, including the legs. The EMG findings can support the diagnosis of SPS by demonstrating abnormal continuous muscle activity in the tested muscles. An EMG may also help distinguish SPS from other neuromuscular disorders. EMG testing can be uncomfortable, though not to the extent that it requires sedation or pain medication. In fact, it is important that patients avoid sedation and refrain from using muscle relaxants or pain medication in advance of an EMG, as use of these drugs can interfere with accurate EMG results.

Imaging Not As Useful In Diagnosis

Imaging studies such as x-rays, CT scans, MRIs, and ultrasounds do not have findings that are unique to SPS, though may be ordered by your doctor to evaluate for other possible disorders.

Disclaimer: The content of this Website is provided for informational and educational purposes only, and does not in any way intend to substitute for professional medical advice, diagnosis, or treatment. The content is not intended to be medical advice for any particular person or patient and should not be relied upon as medical advice. You should always seek the advice of a physician or other qualified healthcare provider for medical advice, including any questions you may have regarding diagnosis or treatment of any medical condition.

Contributors to this document include: Jim Weiss, MD; Vered Lewy-Weiss, MD; Tara Zier, DDS and SPS patient.

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