A case of pseudohypoparathyroidism with diagnostic dilemmas
A Kennedy, DR Hadden & SJ Hunter
A 22 year old female was referred for investigation of cramps in both hands, and tingling in her face. She also complained of lethargy and occasional dizziness. Routine testing by her General Practioner had demonstrated a low serum calcium. She had had problems at birth with hypocalcaemia. A diagnosis of hypothyroidism had been made previously, but she had stopped taking thyroxine medication. Both her mother and grandmother had required intermittent calcium supplementation. On physical examination Trousseau's and Chvostek's sign were positive. She was short in stature and overweight, BMI 30 Kg/m2, but had no brachydactyly. She was clinically euthyroid. Serum calcium was 1.41 mmol/l, serum phosphate 1.68 mmol/l, and serum parathyroid hormone was 211 pg/ml (normal 10-50). Renal function, including magnesium, was normal. Serum Free Thyroxine 8.7 pmol/l (normal 7.6-19.7), TSH 2.9 mU/L (normal 0.45-4.5), LH 4.6 U/L, FSH 6.2 u/L, Oestradiol 94 pmol/l, 0800h cortisol 658 nmol/l, and serum prolactin 139 mU/l. Serum Vitamin D was 29 nmol/l (normal 23-113). Anti-thyroid and anti-adrenal antibodies were negative. A coeliac disease antibody profile and a small bowel series were normal. X-ray of hands and lumbar spine was normal. In view of the evidence of end-organ resistance to parathyroid hormone, a diagnosis of pseudohypoparathyroidism was made. The absence of features of Albrights Hereditary Osteodystrophy suggest this is either Type 1B or Type 2. It has not yet been possible to obtain recombinant PTH to perform an Ellsworth Howard test. However, mutation screening for the GNAS-1 gene is planned to clearly delineate the form of pseudohypoparathyroidism. Family members have been screened and found to have normal serum calcium values.
We present an unusual case of hypocalcaemia in a female, due to isolated resistance to PTH which illustrates some difficulties encountered in confirming a detailed diagnosis due to inability to perform some standard investigations.