A 27-year-old woman presented with bilateral renal stone disease and fracture of the right tibia following trivial trauma. On examination, her blood pressure was 124/80 mm Hg. She had grade I diffuse goitre. She had proptosis of the right eye (23 mm), with 0/7 clinical activity score (fig 1A) and had no features of hyperthyroidism. She did not have any palpable bony swelling or café au lait macules. On investigation, serum calcium was 3.25 mmol/l (normal 2.15–2.55 mmol/l), inorganic phosphorus 0.77 mmol/l (0.87–1.39 mmol/l), serum alkaline phosphatase 66.1 μmol/l (0.67–2.02 μmol/l) and serum parathyroid hormone (iPTH) 1295 ng/l (15–65 ng/l), suggestive of primary hyperparathyroidism. Her thyroid function tests T3 (tri-iodothyronine) 2.26 nmol/l, T4 (thyroxine) 71.75 nmol/l, TSH (thyroid stimulating hormone) 3.84 mU/l, and anti-thyroid peroxidase antibody values (6.36 U/l) were normal. Ultrasound of the neck and technetium 99m MIBI scan localised a left superior parathyroid adenoma. Non-contrast computed tomography (CT) revealed a lytic expansile lesion involving the right orbit, suggestive of osteitis fibrosa cystica (OFC), while the orbital muscles were normal (fig 1B). The patient underwent uneventful curative parathyroidectomy. Three months later, the proptosis had regressed (23 to 21 mm) (fig 2A) and a CT scan of the orbit revealed healing of the lytic bone lesion (fig 2B).
Osteitis fibrosa cystica lesions are usually present in cortical and flat bones and are manifestations of parathyroid hormone (PTH) excess. Involvement of the orbital bones have been scarcely reported.1,2 There are reports of OFC involving the frontal and lacrimal bones, presenting as unilateral exophthalmos. Fine needle aspiration cytology (FNAC) was performed in one of these cases and confirmed to be OFC. However, this procedure is possible only if the lesion is accessible. In our case this could not be performed, but the decrease in proptosis and filling up of the lesion on imaging after curative parathyroidectomy confirms it as a disease related process.