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The significance of low serum thyrotropin in the elderly.

To the Editor. — Sundbeck et al 1 in their unsuccessful search for the causes of a low thyrotropin level in the elderly confined attention to the thyroid gland. A low thyrotropin level, however, is also a feature of panic disorder, where 22% of patients have been shown to have an undetectable level. 2 This could conceivably be linked to the concomitantly elevated level of epinephrine in this disease, 3,4 as its interactions with thyroid hormones have been extensively documented. 5 Thus, the levels in question may have been secondary not to thyrotoxicosis, but to adrenotoxicosis. Studies of adrenal function might provide an answer to this interesting question.