Pathological ankle fracture due to brown tumour: atypical presentation of low serum vitamin D with normal parathyroid hormone and bone profile.

Osteoclastomas or brown tumours are named as such due to increased vascularity, subsequent haemorrhage and haemosiderin deposition giving the lesion a reddish brown appearance under gross microscopic examination. It is due to an increase in parathyroid hormone activity from several causes, such as parathyroid adenomas, renal impairment and low vitamin D levels. The lesions increase the tendency of the bone to fracture. The challenging aspect of the diagnosis is that a histological diagnosis without immunohistochemistry is impossible to make. This is because, without special staining, brown tumours cannot be differentiated from giant cell tumours, which are also classed as benign but can be locally destructive and has potential for malignant transformation. Once tissue diagnosis is confirmed as a brown tumour, then aggressive forms of treatment are not needed, and they generally resolve once the underlying cause is treated. We describe a woman in her 80s who presented to the local Orthopaedic service with a pathological ankle fracture due to a brown tumour.