Choi Decroos E, Hobson-Webb LD, Juel VC, Massey JM, Sanders DB. Do acetylcholine receptor and striated muscle antibodies predict the presence of thymoma in patients with myasthenia gravis?. Muscle Nerve. 2014;49(1):30-34. doi:10.1002/mus.23882

Do acetylcholine receptor and striated muscle antibodies predict the presence of thymoma in patients with myasthenia gravis?

This is a comparative study published in 2014 in the journal of Nerve and Muscle and is on Medline. The researchers retrospectively reviewed 1141 patients seen in the Duke Myasthenia Gravis clinic since July 1, 1980 up to October 1, 2010. Diagnosis for these patients were verified by clinical presentation, response to treatment, antibody testing, and electrodiagnostic studies, including repetitive nerve stimulation and single-fiber electromyography. The researchers goal was to determine a possible correlation between the development of a thymoma with the presence of acetylcholine receptor (AChR) and striated muscle antibodies (StrAbs). AChR binding, blocking, and modulating antibodies and StrAbs are frequently measured in the diagnostic work up for MG.

Diagnosis of thymoma was determined by CT chest imaging and histopathological examination after thymectomy. Patients were also further divided based on early-onset MG (before 40 y/o) and late-onset MG (after 40 y/o). Calculations of positive predictor values for thymoma were by dividing the number of patients with thymoma who had an antibody by the number of all patients who had the antibody. Negative predictive value was calculated by dividing the number of patients without thymoma who did not have an antibody by the number of all patients who did not have the antibody. Only 95 out of 1141 patients had a confirmed thymoma.

In this study myasthenic patients of all age groups without AChR binding antibodies were very unlikely to have a thymoma. The calculated NPV of negative AChR binding antibody was 100% in EOMG and 99.5% in LOMG. The percentage of MG patients with StrAbs increases with age, even in the absence of thymoma. Additionally StrAbs rarely found in EOMG patients without thymoma. Therefore the PPV for thymoma was higher in patients with EOMG and surgery is more often considered with early onset. Higher StrAb levels predict an increased likelihood of thymoma, however the PPV of StrAb for thymoma is lower in the LOMG population. The data showed that several of LOMG patients without thymoma had very high StrAb levels. Although these binding antibodies are not diagnostic for thymoma, elevated levels in EOMG should raise the clinical suspicion and warrant further work up.