Sarcoidosis is a systemic disorder of unknown etiology, characterized by non-caseating granulomas. Hypercalcemia is often a feature secondary to extra-renal dysregulated production of calcitriol (1,25-VitD) by alveolar marcophages within the granulomas. Sarcoid granulomas also produce angiotensin-converting enzyme, with serum ACE levels elevated in 60% of patients. As a diagnostic test however, serum ACE lacks both sensitivity and specificity.
Common thoracic manifestations on HRCT are perilymphatic nodularity with an upper and mid-zone distribution and hilar and mediastinal lymphadenopathy. The 1-2-3 sign refers to bilateral hilar and right paratracheal lymph node enlargement.