A 38-year-old woman from rural Maharashtra presents with a 3-month history of progressive dyspnea, dry cough, and low-grade fever. On examination, she has bilateral hilar lymphadenopathy and erythema nodosum on her shins. Chest X-ray shows bilateral hilar and mediastinal lymphadenopathy with right paratracheal involvement. Serum calcium is 11.2 mg/dL (normal 8.5–10.5). A transbronchial lung biopsy shows non-caseating granulomas with multinucleated giant cells. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Sarcoidosis ### Key Diagnostic Features **Key Point:** The combination of non-caseating granulomas on biopsy, bilateral hilar lymphadenopathy, erythema nodosum, and hypercalcemia is pathognomonic for sarcoidosis. ### Pathological Findings Sarcoidosis is characterized by: 1. **Non-caseating (non-necrotizing) granulomas** — the hallmark histological feature 2. Multinucleated giant cells (both Langhans and foreign-body types) 3. Absence of central necrosis (unlike tuberculosis) 4. Minimal fibrosis in early disease ### Clinical Presentation | Feature | Sarcoidosis | TB | Histoplasmosis | |---------|-------------|----|-----------------| | Granuloma type | Non-caseating | Caseating | Non-caseating | | Hypercalcemia | Common (10–17%) | Rare | Rare | | Erythema nodosum | Frequent | Rare | Rare | | Löfgren syndrome | Yes (acute form) | No | No | | Geographic predilection | Worldwide | High TB burden areas | Ohio/Mississippi valleys | **High-Yield:** Hypercalcemia in sarcoidosis results from extrarenal 1α-hydroxylase activity in activated macrophages within granulomas, producing calcitriol (active vitamin D). ### Löfgren Syndrome (Acute Sarcoidosis) This patient's presentation fits the classic triad: 1. Bilateral hilar lymphadenopathy 2. Erythema nodosum 3. Arthralgia (polyarthritis of ankles/knees) **Clinical Pearl:** Löfgren syndrome has an excellent prognosis with spontaneous remission in >90% of cases within 2 years. ### Why Non-Caseating Granulomas? The absence of central necrosis distinguishes sarcoidosis from TB. The mechanism involves: - Th1/Th17-mediated immune response - Accumulation of epithelioid histiocytes and lymphocytes - Formation of tight, compact granulomas without tissue destruction **Mnemonic for Granulomatous Diseases — CHINA:** Coccidioidomycosis, Histoplasmosis, Inflammatory bowel disease, Noncaseating (Sarcoidosis), Aspergillosis ### Diagnostic Confirmation - **ACE level:** Often elevated (not specific, but supportive) - **24-hour urine calcium:** Elevated due to hypercalcemia - **Chest imaging:** Löfgren pattern (bilateral hilar + right paratracheal lymphadenopathy) - **Transbronchial biopsy:** Gold standard for lung involvement **Warning:** Do not confuse non-caseating granulomas of sarcoidosis with the caseating granulomas of TB — this is a common exam trap.