PRIMARY HYPOTHYROIDISM DISCLOSING PSEUDOH YPOPARATHYROIDISM WITHOUT HYPOCALCEMIA

Background. - Type Ia pseudohypoparathyroidism is due to a molecular d efect causing Gs protein deficiency. It is responsible for multi-hormo nal resistance and skeletal abnormalities. Parathyroid hormone resista nce can be subtle so that the diagnosis can be difficult in patients w ith atypical manifestations. Case report. - A 10-year-old boy was firs t referred for growth retardation (height standard deviation score: -2 ,8). He had short metacarpals, and scaphocephaly. Laboratory findings revealed an elevation of plasma TSH (8,8 mu U/mL) with normal thyroid hormone levels. The investigations ruled out common causes of compensa ted hypothyroidism. Despite normal blood calcium and phosphate levels, parathyroid hormone was elevated to 358 pg/mL (normal values: 10-60) without renal failure, suggestive of hormonal resistance. The diagnosi s of pseudohypoparathyroidism type Ia was confirmed by a 50% reduction of Gs activity. Melanodermia, associated with an elevation of ACTH wa s suggestive of ACTH resistance without MSH resistance. Moreover, skel etal radiography showed a narrow lumbar canal. Conclusion. - Type Ia p seudoypoparathyroidism could be part of the etiological diagnosis of p rimary hypothyroidism, even in the absence of hypocalcemia and hyperph osphatemia. Similarly, skeletal abnormalities extend beyond the classi cal features of Albright's osteodystrophy.