title: Elevated free thyroxine and non-suppressed thyrotropin.
abstract: A young man was diagnosed with hyperthyroidism 10 years prior to current presentation after a random health screening revealed an elevated free thyroxine (fT4) of 36.9 pmol/L. During that time, he saw multiple physicians and was treated with carbimazole intermittently. His repeat thyroid function tests showed persistently elevated fT4 ranging 25-35.7 pmol/L and non-suppressed thyroid-stimulating hormone (TSH) concentrations of 6.78-22.1 mIU/L. He had a smooth, firm and non-tender goitre. At our institution, laboratory interference was first excluded by serial dilution study (TSH) and retesting of TSH and fT4 on alternate assay, which gave reproducible results. His normal α-subunit and sex hormone binding globulin, partially suppressed TSH by high dose triiodothyronine (T3), and positive TSH response to thyrotropin-releasing hormone stimulation were consistent with resistance to thyroid hormone syndrome. The diagnosis was confirmed by direct sequencing of thyroid hormone receptor-β gene, revealing a heterozygous R320 L mutation that causes reduced T3 affinity and reduced corepressor dissociation.
authors.affiliation: Department of Medicine, National University Hospital, Singapore, Singapore.
authors.forename: Shao Feng
authors.initials: SF
authors.lastname: Mok
authors.forename: Tze Ping
authors.initials: TP
authors.lastname: Loh
authors.forename: Byrappa
authors.initials: B
authors.lastname: Venkatesh
authors.forename: Doddabele Srinivasa
authors.initials: DS
authors.lastname: Deepak
mesh_terms: D000328:Adult; D002231:Carbimazole / Q000627:therapeutic use; D004351:Drug Resistance / Q000235:genetics*; D005500:Follow-Up Studies; D020022:Genetic Predisposition to Disease; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood* / Q000175:diagnosis / Q000188:drug therapy* / Q000235:genetics; D008297:Male; D010375:Pedigree; D011433:Propranolol / Q000627:therapeutic use; D012720:Severity of Illness Index; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000097:blood* / Q000378:metabolism; D013974:Thyroxine / Q000097:blood* / Q000378:metabolism; D017211:Treatment Failure
chemical_list: D002231:Carbimazole; D013972:Thyrotropin; D011433:Propranolol; D013974:Thyroxine