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

Abstract

Abstract. 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 < 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 < 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 < 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 < 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 < 0.01) of that in controls, suggesting some degree of hyperthyroidism in liver tissue. One patient was re-investigated after complete remission, which resulted in normalization of T4 and T3 production and mean transit time, as well as serum sex hormone binding globulin levels. The data demonstrate that patients with untreated small cell carcinoma of the lung have enhanced turnover of thyroid hormones, a pattern quite different from that usually seen in non-thyroidal somatic illness.