A 45-year-old woman presents with progressive dyspnoea and bilateral hilar lymphadenopathy on CXR. HRCT shows perilymphatic nodules along bronchovascular bundles, fissures, and subpleural regions. Serum ACE is elevated and serum calcium is 11.0 mg/dL. Which diagnosis is most consistent?

• A Hypersensitivity pneumonitis
• B Lymphangitic carcinomatosis
• C Pulmonary Langerhans cell histiocytosis
• D Sarcoidosis ✓

Explanation

Sarcoidosis classically presents with bilateral hilar lymphadenopathy, perilymphatic nodule distribution on HRCT (along bronchovascular bundles, fissures, and pleural surfaces), elevated ACE, and hypercalcaemia (due to activated macrophage 1-alpha-hydroxylation of vitamin D). The perilymphatic pattern is distinct from random (metastatic/miliary) or centrilobular (HP) distributions. Langerhans cell histiocytosis shows centrilobular nodules with cysts in upper lobes.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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