Bone Abstracts

Background: A 15 year old boy with antenatally diagnosed osteogenesis imperfecta (OI) was reviewed following concerns about poor linear growth, lack of pubertal development and persistent deciduous teeth. He had a history of crush fractures of L1–L2 and previous intra-medullary rodding of his right femur and had been on oral bisphosphonates (Risedronate 70 mg once weekly). He was significantly short (height SDS −4.9), substantially below his genetic potential (target height range 9^th–25^th centiles) and obese (BMI 35.4 kg/m², +3.2 SDS). On examination he had clinical features consistent with OI including blue sclera, ligamentous laxity and dentinogenesis imperfecta with delayed secondary dentition. However, he also had generalised increased subcutaneous adiposity, a dorsal fat pad and pink abdominal striae. He appeared hypothyroid with sallow complexion, dry skin and bradycardia and was pre-pubertal (testicular volumes 3 ml bilaterally) leading to a clinical suspicion of hypopituitarism.

Clinical management: Hypopituitarism was confirmed on biochemical investigations with secondary hypothyroidism (fT₄ 9.3 pmol/l, TSH 0.04 mU/l), low gonadotrophins (LH 0.6 U/l, FSH 2.9 U/l), testosterone (<0.5 nmol/l), IGF1 (<5 nmol/l) and peak growth hormone (GH) concentrations (0.05 mcg/l) on a primed arginine stimulation test (once hypothyroidism corrected with levothyroxine). He also had delayed bone age and a small anterior pituitary with ectopic posterior pituitary on MRI. Bone mineral density (BMD) around the time of GH initiation showed lumbar BMD −1.7 S.D. and total body BMD −1.5. Testosterone gel was introduced 18 months after GH to allow a longer period of growth. Height improved from −4.9 SDS at diagnosis of hypopituitarism to −1.6 SDS (164 cm) at 19 years (lower end of the predicted target centiles).

Discussion: Good growth response to GH was seen, despite late treatment. Hypothyroidism, GH deficiency and hypogonadism will have affected his BMD. The key learning point from this case is that OI alone may not explain significant short stature. In this case, clinical findings were suggestive of an additional diagnosis and it is important to consider the possibility of a second pathology in children with short stature out of keeping with the severity of OI.

Disclosure: The authors declared no competing interests.