'Tiger woman sign' hypercalcaemia: a diagnostic challenge.

Hypercalcaemia is a common electrolyte abnormality with 90% of cases due to either primary hyperparathyroidism or malignancy. Other causes of hypercalcaemia often require careful consideration. We describe an approach to the assessment of hypercalcaemia, particularly where preliminary tests are inconclusive.This approach is illustrated by a case which posed a diagnostic challenge: a patient with significant hypercalcaemia due to acute atypical isolated sarcoid myositis. This case highlights an under-recognised clinical syndrome with distinct biochemical and radiological findings. © Royal College of Physicians 2021. All rights reserved.