Correlation between serum myoglobin and thyroid status in myasthenia gravis.

In 52 patients with myasthenia gravis serum myoglobin showed a significant inverse correlation to circulating thyroxine and triiodothyronine levels. The highest myoglobin concentration (240 ng/ml) was found in a myasthenia gravis patient with hypothyroidism. Slightly elevated myoglobin (54-60 ng/ml) was measured in four euthyroid myasthenic patients. The data suggest that a concomitant hypothyroid state must be excluded whenever high myoglobin levels are found in myasthenia gravis.