Subcutaneous Calcification and Fixed Flexion Deformity of the Right Elbow Joint in a Child with a GNAS Mutation: A Case Report.

Introduction: The art of medicine glorifies when a clinician listens carefully to the patient's story, gives a thorough examination, performs appropriate investigations, and finally links findings together to reach a definite diagnosis. An interesting case was reported here, highlighting the integration of different symptoms and manifestations with some relevant biochemical investigations to reach a final diagnosis. To the best of our knowledge, fixed flexion deformity, as a complication of subcutaneous calcification, has not been previously reported in a child with Albright hereditary osteodystrophy (AHO).

Case presentation: A 2.5-year-old boy was born at term with a birth weight of 3.5 kg (-0.49 SDS). The child was referred to a general pediatrician with a history of right elbow joint swelling noticed initially at six months of age. He then developed the limitation of right upper arm movement, which slowly progressed afterward. The patient had no history of trauma. At nine months of age, he was diagnosed with hypothyroidism, preceded by cold skin, dry hair, and constipation. At nine years of age, he presented with a fixed flexion deformity of the right elbow associated with markedly limited joint movement and symmetrical hands with hyperpigmented knuckles of right metacarpal bones. Subcutaneous masses were felt along the right forearm, showing tenderness on palpation. Investigations revealed elevated serum parathyroid hormone and normal calcium indicating parathyroid hormone resistance. Further genetic testing revealed GNAS mutation. The child was obese throughout his childhood.

Conclusions: This case report describes an obese child with subcutaneous calcification that led to fixed flexion deformity of the elbow, starting at an incredibly early age. Hypothyroidism and pseudohypoparathyroidism raised the suspicion of AHO, which was later confirmed by genetic testing. This is the first case report on fixed flexion deformity in a patient with GNAS mutation (c.719-1G > A Chr20: 57484737) in West Asia.