Endocrine Abstracts

Introduction: Osteitis fibrosa cystica (OFC) or brown tumour is a non-neoplastic fibrocystic expansile lytic bone lesion caused due to excess parathormone (PTH). Brown tumour is classically known to occur in severe primary or secondary hyperparathyroidism due to end-stage renal failure with very high PTH level. OFC presenting as a mass due to nutritional vitamin D deficiency (NVD) is exceedingly rare.

Case presentation: 47-year-old Caucasian gentleman presented with symptoms of generalised bone pain, particularly in the back and right knee progressing over two years with declining mobility but denied tingling, numbness or spasm. He is a strict vegetarian by choice with a significant past history of Vitamin B12 deficiency anaemia. Clinical examination revealed profound kyphoscoliosis causing 19 cm height loss and a warm tender 6 cm swelling arising from the lateral aspect of proximal right tibia. He had diffuse tenderness in the pelvis and lumbar spines and exhibited positive Gower’s sign. Serum bone profile is shown belowImaging studies confirmed a cavitating lesion in the tibia and several areas of lytic lesion at other bony sites. In view of radiological suspicion of malignancy, biopsy of the tibial lesion was performed which showed extensive bone remodelling with areas of cellular and focally haemorrhagic stroma rich in osteoclast giant cells consistent with brown tumour. He was treated with high dose intramuscular Ergocalciferol and went on to develop hungry bone syndrome, requiring parenteral calcium infusion.

Discussion: NVD induced brown tumours are extremely rare in the developed world due to fortification of food,. Hence only a handful of cases are reported in high risk individuals with poor dietary intake, malabsorption disorders and poor exposure to sunlight due to dressing habit. This gentleman was house-bound and completely lacked vitamin D containing foods in his diet for several years leading to this unusual presentation. Radiologically, OFC can be challenging to distinguish from primary bone tumor. Bone biopsy remains the gold standard for diagnosis. The mainstay of treatment is medical with correction of vitamin D and calcium supplementation during the acute phase to prevent hungry bone syndrome. Thorough education and long-term maintenance with Vitamin D supplements should be pursued in high risk individuals.