Objective: Central hypothyroidism (CH) is a well-known adverse effect of bexarotene treatment for cutaneous T-cell lymphoma (CTCL). While concomitant levothyroxine therapy is recommended in these cases, associations between ethnic variation or susceptibility and bexarotene-induced CH have not yet been reported. This study aimed to characterize the kinetics and dose dependency of bexarotene-induced CH in Japanese patients.
Design and patients: Sixty-six Japanese patients with CTCL were retrospectively investigated by evaluating thyroid function during the early phase of bexarotene therapy.
Results: At one week after bexarotene initiation, TSH and FT4 values significantly declined. However, this effect was not bexarotene dose-dependent at least at the dose of 96-320 mg/m2 . Approximately 1 month later, 61 patients exhibited hypothyroidism at a relatively low dose of bexarotene (average 251 mg/m2 /day). Forty-five study cases showed this effect at 1 week. Simple regression analyses indicated that higher pretreatment TSH values (at a cut-off value of 1.30:73% sensitivity, 57% specificity) or lower normal (within the lower half of the reference range) pretreatment FT4 values (84% sensitivity, 57% specificity) were predictive of hypothyroidism at 1 week. The remaining 21 cases showed euthyroidism at 1 week, at which TSH values may roughly predict their thyroid function at 1 month (at a cut-off value of 0.05:100% sensitivity, 80% specificity).
Conclusions: Preventive treatment with levothyroxine is recommended for Japanese CTCL patients prior to bexarotene therapy. Minimally, it should be considered for patients with a pretreatment TSH above 1.30, a lower normal pretreatment FT4, or a TSH below 0.05 at 1 week.
Keywords: RXR agonist; bexarotene; central hypothyroidism; cutaneous T-cell lymphoma; levothyroxine; preventive treatment; thyroid hormone metabolism.
© 2019 John Wiley & Sons Ltd.