[Primary hypothyroidism revealing pseudohypoparathyroidism without hypocalcemia and hyperphosphoremia]

Type la pseudohypoparathyroidism is due to a molecular defect causing Gs protein deficiency. It is responsible for multi-hormonal resistance and skeletal abnormalities. Parathyroid hormone resistance can be subtle so that the diagnosis can be difficult in patients with atypical manifestations.

A 10-year-old boy was first 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 microU/mL) with normal thyroid hormone levels. The investigations ruled out common causes of compensated 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 diagnosis of pseudohypoparathyroidism type la was confirmed by a 50% reduction of Gs activity. Melanodermia, associated with an elevation of ACTH was suggestive of ACTH resistance without MSH resistance. Moreover, skeletal radiography showed a narrow lumbar canal.

Type la pseudoypoparathyroidism could be part of the etiological diagnosis of primary hypothyroidism, even in the absence of hypocalcemia and hyperphosphatemia. Similarly, skeletal abnormalities extend beyond the classical features of Albright's osteodystrophy.