Thyroid hormone turnover in patients with small cell carcinoma of the lung

Patients with small cell carcinoma of the lung often present with symptoms suggestive of hyperthyroidism i.e. weight loss without anorexia. Consequently [125I]T4 and [131I]T3 turnover was studied using simultaneously iv bolus injection and noncompartmental analysis in 6 patients with untreated small cell carcinoma of the lung and 14 normal subjects of comparable ages. Both T4 and T3 production rates were enhanced, T4 production being in median 135 nmol.day-1.70 kg-1 (range 111-200) in patients with small cell carcinoma of the lung vs 98 nmol.day-1.70 kg-1 (range 69-134) in controls (P less than 0.01), and T3 production being 46 nmol.day-1.70 kg-1 (range 33-65) vs 31 nmol.day-1.70 kg-1 (range 24-45) (P less than 0.01). The mean transit time was shortened for both T4 and T3, T4 mean transit time being 5.9 days (3.9-8.0 days) vs 8.3 days (6.1-11.2 days) in controls (P less than 0.01), and T3 mean transit time being 0.74 days (0.36-0.98 days) vs 1.03 days (0.81-1.45 days) in controls (P less than 0.01). Serum total and free T4 and T3 levels were unchanged. Basal serum TSH levels and the TSH response to iv TRH were also normal. Thyroid-stimulating immunoglobulins were only present in the serum in 1 of 6 patients. Thus, thyroid hormone production seemed under pituitary regulation. The peripheral effect of thyroid hormones was evaluated measuring serum sex hormone binding globulin levels, which were increased to in median 270% (77-310%) (P less than 0.01) of that in controls, suggesting some degree of hyperthyroidism in liver tissue.(ABSTRACT TRUNCATED AT 250 WORDS)