Congenital hypothyroidism--correlation between radiographic appearances of the knee epiphyses and biochemical data.

Plain knee radiographs of 20 neonates with congenital hypothyroidism, were reviewed. The size and appearances of the epiphyses were compared with the biochemical data at the time of referral. Fifteen infants had unequivocal evidence of delayed bone maturation based on absence of the distal femoral epiphysis or small epiphyseal size. Seven cases had fragmentation of at least one epiphysis. A positive correlation was found, at diagnosis, between the thyroxine and triiodothyronine levels and the size of the knee epiphyses. All 14 infants with thyroxine levels of less than 70 nmol/l had small epiphyses with a combined mean diameter of the proximal tibial plus distal femoral epiphyses of 7 mm or less. Conversely, of the 6 infants with thyroxine levels of 70 nmol/l or above, 5 had combined epiphyseal diameters of greater than 10 mm. We suggest that in infants with no clinical symptoms and only moderately raised raised screening thyroid stimulating hormone, a knee radiograph showing the described radiological changes should prompt institution of thyroxine treatment before awaiting biochemical confirmation of the diagnosis.