What is sarcoidosis?

What is Sarcoidosis?

Sarcoidosis is a multisystem inflammatory disease of unknown cause characterized by nonnecrotizing granulomatous inflammation that can affect virtually any organ, most commonly the lungs and intrathoracic lymph nodes. 1

Core Diagnostic Features

The diagnosis of sarcoidosis rests on three essential criteria 1:

• Compatible clinical presentation with variable manifestations ranging from asymptomatic disease to progressive, life-threatening organ involvement 1
• Histological evidence of nonnecrotizing granulomatous inflammation in affected tissues (though not always required for certain highly specific presentations) 1
• Exclusion of alternative causes of granulomatous disease, including infections (particularly tuberculosis), malignancy, berylliosis, and drug-induced granulomatous reactions 1

Pathological Hallmarks

The characteristic sarcoid granuloma consists of well-formed, concentrically arranged immune cells with a central core of macrophage aggregates and multinucleated giant cells, surrounded by loosely organized lymphocytes (predominantly T cells) 1. These granulomas are typically nonnecrotic, though the nodular pulmonary phenotype may present with mixed necrotic and nonnecrotic granulomas 1. The granulomas demonstrate a perilymphatic distribution, clustering around bronchovascular bundles, fibrous septa containing pulmonary veins, and the visceral pleura 1.

Clinical Presentation Spectrum

Highly Specific Presentations (Diagnostic Without Biopsy)

Certain clinical syndromes are so characteristic that they establish the diagnosis without requiring histological confirmation 1:

• Löfgren's syndrome: Acute presentation with bilateral hilar lymphadenopathy, erythema nodosum, and arthritis 1
• Lupus pernio: Chronic, violaceous skin lesions typically affecting the nose, cheeks, and ears 1
• Heerfordt's syndrome: Parotid gland enlargement, uveitis, facial nerve palsy, and fever 1

Common Organ Involvement

Intrathoracic disease occurs in approximately 90% of patients, manifesting as bilateral hilar adenopathy and/or diffuse lung micronodules with perilymphatic distribution 2. The Scadding radiographic staging system correlates with prognosis: Stages I-II have 30-80% spontaneous remission rates, Stage III has 10-40% resolution, while Stage IV (fibrotic disease) has no chance of resolution 3.

Extrapulmonary manifestations with 25-50% prevalence include 2:

• Skin lesions (maculopapular, erythematous, or violaceous lesions; subcutaneous nodules) 1
• Uveitis and other ocular involvement 1
• Peripheral lymphadenopathy 2
• Hepatic and splenic involvement 1
• Peripheral arthritis 2

Less common but high-morbidity manifestations (affecting <10% of patients) include cardiac involvement, neurological disease, hypercalcemia/hypercalciuria, and renal dysfunction 2.

Epidemiology and Prognosis

Sarcoidosis affects 2-160 per 100,000 people worldwide, with higher prevalence in African Americans and Scandinavians, typically presenting in adults aged 30-50 years 2, 4. The 5-year mortality rate is approximately 7%, with African American women experiencing 2.4-times higher mortality compared to matched controls without sarcoidosis 1, 3.

Approximately 60% of sarcoidosis deaths are directly attributable to the disease, with up to 80% of these resulting from advanced cardiopulmonary failure, including pulmonary hypertension and respiratory infections 3. In Japan, over 70% of sarcoidosis deaths result from cardiac involvement 3.

Progressive Disease

Up to 40% of pulmonary sarcoidosis patients progress to Stage IV disease with lung parenchymal fibrosis, bronchiectasis, hilar retraction, and fibrocystic changes 3. These patients face the highest mortality risk, with up to 70% developing precapillary pulmonary hypertension and 5-year mortality exceeding 40% when significant fibrosis (>20% on HRCT) or pulmonary hypertension is present 3.

Key Diagnostic Pitfalls

Critical differential diagnoses that must be excluded include 1:

• Chronic beryllium disease: Histologically identical to sarcoidosis; requires blood lymphocyte proliferation test for differentiation 1
• Tuberculosis: Accounts for 38% of alternative diagnoses in patients with suspected Stage I sarcoidosis 1
• Lymphoma: Represents 25% of alternative diagnoses in bilateral hilar lymphadenopathy cases 1
• IgG4-related disease: Can be differentiated by elevated serum IgG4 levels (high IgG4:IgG ratio in ~66% of cases) and distinct pathological features 1
• Drug-induced granulomatous reactions: Associated with immune checkpoint inhibitors, anti-TNF-α agents, and other immunotherapeutics 1

Supporting Diagnostic Features

Highly probable clinical features include bilateral hilar adenopathy on imaging, perilymphatic nodules on chest CT, gadolinium enhancement on CNS MRI, and characteristic bone lesions 1. Laboratory findings such as elevated ACE levels, BAL lymphocytosis with elevated CD4:CD8 ratio, and hypercalcemia with abnormal vitamin D metabolism support the diagnosis but are not specific 1.

Treatment Implications

The decision to treat depends on two major factors: risk for death or organ failure and impairment of quality of life 1. Oral glucocorticoids (prednisone 20-40 mg daily) remain first-line therapy for symptomatic disease with parenchymal infiltrates and abnormal pulmonary function 3. Second-line agents (methotrexate, azathioprine) and third-line treatments (anti-TNF agents like adalimumab and infliximab) serve as glucocorticoid-sparing alternatives 1, 3, 5. Despite treatment, relapse rates range from 13-75% depending on disease stage, organ involvement, and socioeconomic factors 3.