Fast Five Quiz: Refresh and Test Your Knowledge of Myasthenia Gravis

Amy Kao, MD


July 06, 2021

"Anti-striated muscle antibody" refers to a class of antibodies against intracellular components of skeletal muscle, including titin, the ryanodine receptor, myosin, and alpha-actin. Anti-striated muscle antibody is present in about 70%-80% of patients with thymoma and MG who are younger than 40 years, 30% of adult patients with MG without thymoma, and 24% of patients with thymoma without MG. Thus, a positive test result should prompt a search for thymoma especially in patients younger than 40 years. In individuals older than 40 years, anti-striated muscle antibody can be present without thymoma. It is important to highlight that the presence of anti-striational antibodies alone is not diagnostic for myasthenia gravis as they do not directly impair neuromuscular junction function.

RNS is highly specific and the procedure is easily performed and repeated. Because RNS changes correlate with severity of neuromuscular transmission defect, this approach may be useful in monitoring treatment response. However, the procedure may not be well tolerated in facial and proximal muscles, or by obese patients, and is generally not performed serially.

Routine histopathology is not part of the evaluation of MG. Routine light microscopy reveal mild, nonspecific abnormalities on muscle biopsy, including type 1 fiber predominance, mild fiber type grouping, or type 2 fiber atrophy.

Learn more about the workup of MG.


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