Brown spinal tumour secondary to primary hyperparathyroidism, a primary entity that we should not forget

Introduction: A thorough study of lytic lesions can guide us toward a more accurate aetiology in spinal column lesions. The use of imaging techniques and blood chemistry studies is useful when considering brown tumours as part of the differential diagnosis. Clinical Case: A 43-year-old woman with multiple comorbidities presented with lumbar pain. A lytic lesion in the body of S2 was documented, and thoracoabdominal lesions were initially ruled out. However, during her stay, a malignant thyroid lesion was documented. Discussion: Hyperparathyroidism, whether primary (adenomas, hyperplasia, or carcinoma) or secondary (vitamin D deficiency or chronic kidney disease), causes skeletal alterations in approximately 16% of cases. Among its manifestations are parathyroid tumours, which primarily affect the pelvis, rib arches, facial bones, and long bones, with less frequency in the spine. Clinically, these present progressive pain and neurological deficits. Diagnosis requires paraclinical tests and imaging studies. Treatment should address the underlying cause of hyperparathyroidism, with options ranging from medical therapies to surgical interventions. Conclusion: Thyroid carcinoma as a manifestation of a brown tumour at the sacral level is a rare presentation. We consider it pertinent to perform extension studies when evaluating patients with multiple comorbidities and a single lytic lesion.