Pseudohypoparathyroidism (PHP) is a group of endocrine disorders characterised by resistance to parathyroid hormone (PTH), resulting in hypocalcaemia and hypophosphatemia (1-3). Subtypes of pseudohypoparathyroidism include 1a and 1b (1-4). Clinical features may include early growth plate closure, ectopic ossification, brachydactyly, early obesity, respiratory disorders, and short stature, with variable resistance to other hormones (FSH, TSH, LH, and GHRH) (1-4). Type 1a is associated with Albright's hereditary osteodystrophy (AHO) (1,2). Type 1b, the rarer form, is characterised by renal resistance to PTH (1,2). This case review examines the diagnosis and management of type 1b PHP, highlighting key similarities and differences between the PHP subtypes.
Mrs X is a 55-year-old female who presented with bilateral hip pain and was diagnosed with bilateral femoral head avascular necrosis. Routine biochemistry revealed a calcium of 2.16 mmol/L, a phosphate of 1.0 mmol/L, a vitamin D of 70nmol/L, and an increased PTH of 120 pmol/L. Past medical history included severe asthma, hypertension, hypercholesterolemia, hypothyroidism, Type 2 Diabetes mellitus, sleeve gastrectomy, dental decay, recurrent sinusitis, and renal impairment (atrophic left kidney). CTx, ALP, and P1NP were increased (1678 ng/L, 194 U/L, and 235 U/L, respectively) with mild renal impairment (Cr 98). There was no brachydactyly, and a bone scan showed widespread increased uptake. A diagnosis of probable PHP was made, and genetics confirmed type 1b PHP (methylation at the GNAS locus). She was commenced on calcitriol with the goal of maintaining PTH near the upper limit of normal, with ongoing input from orthopaedics and genetic services.
This case illustrates a relatively rare endocrine bone disorder, which carries a significant burden for patients and can be challenging to diagnose. It highlights the differences between type 1a and b pseudohypoparathyroidism and emphasises the importance of a multidisciplinary approach to care.