Pruritus as the presenting symptom in hyperthyroidism

Abstract

Dear Sir, Pruritus as an occasional complaint in hyperthyroidism was first noted by William Osler in 1904,1 but it has often been forgotten since — despite the assertion that generalised pruritus occurs in 4%–11% of such patients, especially in those with Graves' disease.2 Abnormalities of liver function are often seen in hyperthyroidism.3 Clinical jaundice has been described as a rare complication.4 We present two cases with generalised pruritus as the single or predominant symptom. An 18-year-old girl complained of body itch for 2 years, for which she had been using (futilely) the scabicide lindane (Quellada). She had also experienced 2 months of oligomenorrhoea and increasing appetite. Her biochemical abnormalities included AST 45 IU/l (ref <35), ALT 80 IU/l (ref <40), alkaline phosphatase 1345 IU/l (ref 67–230) and a free T4 of 85.2 pmol/l (ref 9–24). A thyroid scan revealed no nodules and she was treated with carbimazole and propranolol. The itch disappeared and the thyroid function tests and liver transaminase quickly reverted to normal. The alkaline phosphatase level, however, returned only slowly to the reference range, overa 12-month period. Five years later, while off all treatment apart from her combined oral contraceptive (Marvelon), the pruritus returned and she was again thyrotoxic with a free T4 of 98.5 pmol/l, T3 8.22 nmol/l (ref 1.0–3.0), ALT 144 IU/l, alkaline phosphatase 633 IU/l. On commencement of therapy with carbimazole and l-thyroxine the symptoms again immediately abated. A 33-year-old woman presented with a 2-month history of generalised pruritus and vaginal candidiasis treated with an antihistamine and fluconazole. On review within 4 weeks, the itch remained but she had lost about 3.5 kg (8 lbs) in weight and had a fine tremor. Free T4 was 88.7 pmol/l, bilirubin 22 μmol/l, ALT 48 IU/l and alkaline phosphatase 448 IU/l. Carbimazole and l-thyroxine were commenced and the symptoms resolved. Pairitus was described in 8 of 108 cases of hyperthyroidism at the Johns Hopkins Hospital, and the symptom was noted to appear with the disease and disappear with treatment in a small number of patients.5 Rarely, as in our case, pruritus has been noted as the principal presenting complaint.6 The disease mechanism is listed as unknown in Cecil's Textbook of Medicine.7 Cholestasis is suggested by the reported increase in plasma alkaline phosphatase and in BSP retention in other cases.8 The pathogenesis of pruritus in cholestasis is unknown, but anion exchange resins have been used successfully in treatment. These interfere with the enterohepatic circulation of bile acids and other substances which may interact with unmyelinated C nerve endings at or below the dermoepithelial junction.9 The pruritus in these cases acted as an index of thyroxine-induced hepatic dysfunction, and is an unusual primary presenting symptom.