Stiff-Person Disorders Profile, Serum

Serum

2 mL

1 mL (Note: This volume does not allow for repeat testing.)

Gel-barrier tube or red-top tube

This test is recommended for the assessment of stiff-person disorders, whether they manifest in classical or focal forms. This includes symptoms like stiffness, spasms, hyperekplexia, limb rigidity, myoclonus or limb dystonia, regardless of the presence or absence of encephalopathy.

Stiff person syndrome (SPS) primarily results in progressive muscle stiffness (rigidity) and recurrent painful muscle spasms. The rigidity tends to vary, often coinciding with muscle spasms. These spasms can occur spontaneously or be triggered by various stimuli, such as sudden noise, light physical contact or exposure to cold. SPS is an autoimmune disorder and may coexist with other autoimmune conditions like thyroid disease, diabetes, pernicious anemia (B12 deficiency) and vitiligo. The most commonly detected antibody biomarker in the stiff-person spectrum is glutamic acid decarboxylase 65 (GAD65) antibody. Individuals with this syndrome typically exhibit classical or limited stiff-person forms, almost always with antibody values exceeding 20.0 nmol/L. About 50% of these patients have concomitant non-neurological autoimmune diseases, with type 1 diabetes and thyroid disease being the most prevalent, and there is usually an absence of associated cancer. Amphiphysin antibody positivity is frequently observed in individuals with occult breast adenocarcinoma, presenting symptoms such as limb stiffness and spasms. Neurogenic changes are typically detectable during clinical examination and electromyography. Dipeptidyl-peptidase-like protein-6 (DPPX) antibody is linked to diverse central and autonomic presentations. In cases positive for DPPX-IgG, testing for B-cell blood dyscrasias is advisable. Testing in both serum and CSF is recommended to maximize diagnostic yield.

The absence of positive results does not rule out the possibility of a diagnosis of stiff-person spectrum disorder. It is important to interpret the low titer of GAD65 antibody cautiously. GAD65 autoimmunity is linked to other autoimmune conditions that can lead to neurological symptoms, such as type 1 diabetes, pernicious anemia, hypothyroidism and adrenal insufficiency.

This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.

Immunofluorescence, immunoblot