Chronic intestinal giardiasis with isolated levothyroxine malabsorption as reason for severe hypothyroidism--implications for localization of thyroid hormone absorption in the gut.

We report a case of isolated levothyroxine malabsorption in the course of chronic intestinal giardiasis, leading to severe hypothyroidism. Infection with Giardia lamblia was proved histologically by jejunal biopsy. Treatment with metronidazole resulted in complete elimination of parasites and recovery of regular intestinal thyroid hormone absorption. Stable euthyroidism was accomplished with common replacement doses of orally administered levothyroxine.