1511 Open Access J Pak Med Assoc Abstract Brown tumour is an infrequent, focal, and benign osteolytic lesion which is a consequence of abnormal bone metabolism in hyperparathyroidism (both primary and secondary). It is also known as Osteoclastoma. In the present era, we rarely encounter skeletal disease caused by primary hyperparathyroidism. Although it is a rare presentation because of advancement of treatment but still can be encountered because of lack of standard care so we should have high index of suspicion to avoid this preventable complication. We report here a case of brown tumour in the thoracic vertebra of a young female patient with End Stage Renal Disease, who presented with backache and bilateral lower limb weakness. MRI of the spine showed multiple non-enhancing abnormal signals involving vertebral body of C2, posterior elements of C6, and bilateral sacral vertebra, suggestive of healed fractures versus bone forming tumours. She underwent laminectomy. Her histopathology report was consistent with brown tumour of hyperparathyroidism. Keywords: Hyperparathyroidism, brown tumour, laminectomy, osteoclastoma, end stage renal disease. DOI: https://doi.org/10.47391/JPMA.6271 Submission completion date: 28-03-2022 Acceptance date: 02-01-2023 Introduction Hyperparathyroidism (HPT) results in an augmented efflux of calcium from the bones due to which plasma calcium’s concentration is increased, which leads to reduced absorption of calcium by the kidneys and intestine resulting in skeletal demineralisation; hence, the bone is being replaced by osteoclasts (or multinucleated giant cells)which contribute to deformed and labile skeleton. Primary hyperparathyroidism is caused by hyper secretion of the parathyroid hormone due to changes in one or more parathyroid glands. The end result is hypercalcaemia. Secondary hyperparathyroidism is the result of end-stage renal disease (ESRD) in which there is excessive loss of calcium in the urine, which leads to elevation of serum parathyroid hormone level secondary to feedback response to low serum calcium levels. Tertiary hyperparathyroidism is seen in patients who have longstanding chronic kidney disease. In tertiary hyperparathyroidism there is autonomous hyperplasia of the parathyroid glands as there is no feedback response to the level of calcium in serum. The pathognomic feature of hyperparathyroidism is resorption of skeleton which occurs due to augmented activity of osteoclasts. There is accumulation of loose connective tissue inside both cortical and trabecular bones. In some patients, brown tumour of hyperparathyroidism is seen which is a distinct lesion composed of osteoclasts, numerous reactive giant cells and haemorrhagic debris. 1 In end stage renal disease, a variety of bony involvement is seen which is termed as renal osteodystrophy. In our case, HPT was diagnosed by the presence of osteolytic lesions called osteoclastomas or brown tumours. Only a few patients with HPT have radiologically noticeable skeletal changes. The characteristic skeletal manifestations of HPT are mentioned below: (1) Erosions of periosteal surfaces of phalanges of the hands. (2) Ten percent of HPT cases have brown tumours and these usually appear in advanced disease. (3) There are localised regions of bone loss due to augmented osteoclastic activity which leads to loss of architecture of the skeleton; these are termed as Osteitis fbrosa cystica. (4) The skeleton has radiolucent appearance which is secondary to demineralisation. (5) Due to loss of central trabeculae and thinning of the cortex, the skull bones have granular appearance in HPT. 2 (6) Pathologic calcifcations with punctuate appearance are seen in soft tissues, kidneys and joints. In this case report, we present a young female patient with brown tumour of thoracic spine causing spinal cord compression so as to raise its awareness among health care professionals since this is rare but preventable cause of Department of Medicine, Aga Khan University Hospital, Karachi, Pakistan. Correspondence: Saira Furqan. e-mail: saira.furqan@aku.edu ORCID ID. 0000-0002-5526-0673 CASE REPORT Brown tumour as an unusual but preventable cause of spinal cord compression: Case report and literature review Sabiha Banu, Saira Furqan