Thyronine (T4), triiodothyronine (T3), and reverse-triiodothyronine (rT3) levels were evaluated in cerebrospinal fluid (CSF) and in serum of 12 patients with definite amyotrophic lateral sclerosis (ALS) by specific radioimmunoassays. Circulating microsomal and thyroglobulin antibodies were also evaluated. In all patients serum levels of T4, T3 and rT3 were within normal limits. In CSF, the rT3 levels were significantly elevated to 0.118 micrograms/l (mean), the T4 levels were not significantly elevated, and the T3 levels were below the detection limit of 0.03 micrograms/l. A correlation between the elevated rT3 levels in CSF and the severity or type of ALS could not be demonstrated by this study. The antithyroid antibodies (thyroglobulin antibodies, microsomal antibodies) showed normal titres and did not suggest disturbances of thyroid autoimmunity in the patients with ALS.
