Vitamin D deficiency or pseudohypoparathyroidism?

Severe vitamin D deficiency (VDD) typically presents with overt hypocalcemia, hypophosphatemia, high alkaline phosphatase (ALP) and high parathyroid hormone (PTH). The clinical presentation and the biochemical features in atypical cases of VDD can be similar to pseudohypoparathyroidism (PHP). We present 2 patients with atypical laboratory findings of severe VDD secondary to restrictive eating disorders. PHP was considered, given hyperphosphatemia rather than hypophosphatemia classically seen with severe VDD. Renal PTH resistance, mimicking PHP, was observed in both cases with high phosphorus and high PTH levels in the setting of severe VDD. Calcitriol was added to the treatment to normalize serum calcium levels and overcome PTH resistance. Hypocalcemia and hyperphosphatemia resolved and PTH normalized with calcium, cholecalciferol and calcitriol supplementations and dietary modification, eliminating the need for further workup for PHP.