Interpretation

Positive results (>0.02 nmol/L) are indicative of autoimmune myasthenia gravis (MG). These results should be interpreted in the appropriate clinical and electrophysiological context.

With a diagnosis of MG, a paraneoplastic basis should be considered with thymoma being the most frequently associated tumor with MG.

The clinical sensitivity of this assay is approximately 90% in nonimmunosuppressed patients with generalized MG. The frequency of antibody detection is lower in MG patients with weakness clinically restricted to ocular muscles (71%), and antibody titers are generally low in ocular MG (eg, 0.03-1.0 nmol/L).

Negative results do not exclude the diagnosis of MG. If clinical suspicion remains and symptoms persist or worsen consider retesting. Results may be negative in the first 12 months after symptoms of MG appear or during immunosuppressant therapy. Note: In follow up of seronegative patients with adult-acquired generalized MG, 17.4% seroconvert to positive at 12 months (ie, seronegativity rate at 12 months is 8.4%). A subset of MG patients that are persistently negative for acetylcholine receptor binding antibodies will have muscle-specific kinase (MuSK) antibodies, and therefore, it is recommended to test for MuSK antibodies in seronegative patients with high clinical suspicion of MG.

In general, there is not a close correlation between antibody titer and severity of weakness, but in individual patients, clinical improvement may be accompanied by a decrease in titer.