Sarcoidosis

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Sarcoidosis




I. Definition

  • A chronic, multisystem granulomatous disease of unknown cause.

  • Characterized by non-caseating granulomas in affected tissues.

  • Thought to result from dysregulated immune response to unknown antigen(s).

II. Epidemiology

  • Most common in young adults (20–40 yrs).

  • Higher prevalence in African descent and Northern Europeans.

  • Female > Male (slightly).

III. Pathophysiology

  • T-helper cell (CD4⁺) activation in response to antigen → cytokine release (IFN-γ, IL-2).

  • Formation of non-caseating granulomas.

  • Granulomas produce 1-α hydroxylase → ↑ calcitriol (1,25-dihydroxyvitamin D) → hypercalcemia & hypercalciuria.

  • Hypercalcemia is PTH-independent (low PTH, high calcitriol).

IV. Clinical Manifestations

Pulmonary (most common)

  • Dry cough, dyspnea, chest pain.

  • Bilateral hilar lymphadenopathy (classic).

  • Interstitial lung disease → restrictive pattern.

Skin

  • Erythema nodosum (tender red nodules, usually on shins).

  • Papular or plaque-like lesions.

  • Lupus pernio (violaceous nasal/cheek plaques, pathognomonic).

Ocular

  • Uveitis (anterior or posterior) → eye pain, photophobia, blurred vision.

  • Can cause blindness if untreated.

Lymph nodes

  • Generalized lymphadenopathy.

Musculoskeletal

  • Polyarthritis (ankle arthritis common).

Cardiac

  • Arrhythmias, restrictive or dilated cardiomyopathy, conduction abnormalities, sudden death.

Neurologic (neurosarcoidosis)

  • Cranial neuropathies (facial nerve palsy).

  • Hypothalamic-pituitary infiltration → central diabetes insipidus, hypopituitarism.

Renal

  • Hypercalcemia/hypercalciuria → nephrolithiasis, nephrocalcinosis.

V. Laboratory Findings

  • ↑ ACE levels (not specific, but supportive).

  • ↑ Serum calcium, ↑ urinary calcium.

  • ↓ PTH.

  • ↑ Calcitriol (1,25-vitamin D).

  • ↑ ESR, hypergammaglobulinemia.

VI. Imaging

  • Chest X-ray: bilateral hilar lymphadenopathy ± parenchymal infiltrates.

  • High-resolution CT: interstitial lung disease, nodules along bronchovascular bundles.

VII. Diagnosis

  • Clinical + radiologic suspicion.

  • Tissue biopsy: non-caseating granulomas (exclusion of infections like TB/fungal).

  • Must rule out mimickers: tuberculosis, fungal infections, lymphoma.

VIII. Treatment

  • Asymptomatic / mild disease: observation (many remit spontaneously).

  • Symptomatic (pulmonary, ocular, cardiac, neuro, hypercalcemia):

    • Glucocorticoids = first-line.

  • Refractory cases: methotrexate, azathioprine, TNF-α inhibitors.

IX. Key Differentiation: Hypercalcemia in Sarcoidosis vs Primary Hyperparathyroidism

FeatureSarcoidosisPHPT
PTH↓↑
Calcitriol (1,25 Vit D)↑Normal/↓
Urinary calcium↑↑
CauseExtrarenal calcitriol production by granulomasAutonomous PTH secretion

✅ Exam Pearls

  • Bilateral hilar lymphadenopathy + erythema nodosum = classic presentation.

  • Hypercalcemia in sarcoidosis → due to extrarenal calcitriol, not PTH.

  • Always rule out TB before starting steroids.

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