Background and design: After the chance of observation of an elevated parathyroid hormone (PTH) value in a patient with pityriasis rubra pilaris, the serum PTH level was measured in the next 14 patients seen with disorders of keratinization. Calcium metabolism in three affected patients was then studied in depth.
Results: Five of 15 patients had twofold or greater elevations in serum PTH values. The patients had four different disorders of keratinization: bullous congenital ichthyosiform erythroderma (two patients); lamellar ichthyosis (one patient); pityriasis rubra pilaris (one patient); and ichthyosis linearis circumflexa (one patient). At least one other patient with each diagnosis had normal PTH values. Two of three patients who were studied further had clear evidence of increased, biologically active PTH, consistent with secondary hyperparathyroidism. An elevated PTH level spontaneously became normal in one patient, and in a second patient it became normal with a high-calcium diet.
Conclusions: These data provide the first indication that patients with various disorders of keratinization have an increased risk for secondary hyperparathyroidism. The exact prevalence, origin, and physiologic significance of this finding remain to be elucidated.