Sarcoidosis

Detailed Overview

The hallmark of sarcoidosis is an exaggerated CD4+ T-cell mediated immune response to an unidentified antigen, leading to granuloma formation. In the lungs, this causes restrictive lung disease and fibrosis. Symptoms vary widely from asymptomatic incidental findings on chest X-rays (hilar adenopathy) to severe, progressive multi-organ failure. The clinical course is highly variable; roughly two-thirds of patients experience spontaneous remission, while one-third develop chronic, progressive disease.

Epidemiology & Demographics

Highest prevalence in African Americans (up to 35 per 100,000) and Northern European/Scandinavian populations. Typically presents in adults 20-40 years old. Slightly more common in women, who tend to have more severe cutaneous and ocular involvement.

Etiological Mechanism

The exact cause is unknown. It is hypothesized to be an aberrant immune response to an environmental, occupational, or infectious antigen (e.g., Propionibacterium acnes, mycobacterial antigens, or beryllium) in genetically susceptible individuals (HLA-DRB1 alleles).

Primary Causes

Idiopathic. Triggered by unknown airborne antigens inducing a Th1-mediated immune response in the lungs.

• Race and Ethnicity: African Americans have a 3 to 4-fold higher risk and tend to have more severe, chronic, extrapulmonary disease.
• Genetics: Family history increases risk 5-fold; HLA-DRB1*1101 and *1501 are strongly associated.
• Environmental Exposures: Exposure to mold, agricultural dusts, and certain occupational environments (e.g., World Trade Center responders) increases risk.

An unknown antigen is processed by alveolar macrophages and presented to CD4+ T-helper cells. This triggers a massive Th1 response, secreting IL-2, IFN-gamma, and TNF-alpha. These cytokines recruit and activate more macrophages, which aggregate and transform into epithelioid cells and multinucleated giant cells, forming noncaseating granulomas. These granulomas displace normal tissue, causing organ dysfunction. Activated macrophages within the granulomas also express 1-alpha-hydroxylase, an enzyme that converts 25-hydroxyvitamin D to active 1,25-dihydroxyvitamin D, leading to hypercalcemia. Fibroblasts may be recruited, causing irreversible pulmonary fibrosis.

Characteristic Clinical Presentation

• Pulmonary Symptoms: Dry, non-productive cough, insidious onset of dyspnea, and vague chest discomfort.
• Constitutional: Fatigue (often severe and debilitating), fever, night sweats, and weight loss.
• Cutaneous: Erythema nodosum (tender red nodules on shins - good prognosis), lupus pernio (violaceous rash on nose/cheeks - poor prognosis).
• Ocular: Anterior uveitis presenting as eye pain, photophobia, and blurred vision.

Physical Examination Signs

• Lofgren Syndrome
• Heerfordt Syndrome
• Crackles

• Cardiac Sarcoidosis: Granulomas in the myocardium causing restrictive cardiomyopathy, heart block, or fatal ventricular arrhythmias.
• Neurosarcoidosis: Cranial nerve palsies (especially CN VII), meningitis, or pituitary dysfunction.
• Nephrocalcinosis: Chronic hypercalcemia and hypercalciuria leading to kidney stones and renal failure.

Diagnostic Criteria & Guidelines

Requires three elements: 1) Compatible clinical and radiographic presentation, 2) Histological evidence of noncaseating granulomas (via bronchoscopy with transbronchial biopsy or biopsy of skin/lymph node), and 3) Exclusion of other granulomatous diseases (negative AFB stains for TB, negative fungal cultures).

Differential Diagnosis

• Tuberculosis (caseating granulomas)
• Lymphoma (Hodgkin/Non-Hodgkin)
• Berylliosis (indistinguishable pathologically, requires occupational history)
• Histoplasmosis
• Idiopathic Pulmonary Fibrosis

Laboratory Tests & Biomarkers

• Serum ACE (Angiotensin-Converting Enzyme): Elevated in ~60% of patients. Secreted by granulomas, but lacks sensitivity and specificity.
• Calcium Levels: Hypercalcemia and hypercalciuria due to extra-renal calcitriol production.
• CD4/CD8 Ratio in BAL: Bronchoalveolar lavage fluid shows lymphocytosis with a CD4/CD8 ratio > 3.5 (highly specific).

Imaging Modalities & Findings

• Chest X-Ray: Symmetric, bilateral hilar and right paratracheal lymphadenopathy (Garland's triad or 1-2-3 sign). Reticulonodular opacities in upper lobes.
• High-Resolution CT (HRCT): Micronodules clustered along the bronchovascular bundles and subpleural regions. Thickening of interlobular septa.
• Cardiac PET/MRI: Patchy FDG uptake or delayed gadolinium enhancement indicating active myocardial granulomas.

• Stage 0
  Normal chest radiograph, but extrapulmonary involvement present.
• Stage I
  Bilateral hilar lymphadenopathy (BHL) only. Highest rate of spontaneous remission (80%).
• Stage II
  BHL with pulmonary parenchymal infiltrates. 60% remission rate.
• Stage III
  Pulmonary infiltrates without BHL.
• Stage IV
  Pulmonary fibrosis with honeycombing and volume loss. Irreversible.

Second-Line & Adjunctive Therapy

For steroid-refractory disease, steroid-sparing agents are used: Methotrexate 10-15 mg PO weekly, Azathioprine, or Mycophenolate mofetil. Third-line for severe/refractory disease uses TNF-alpha inhibitors like Infliximab 3-5 mg/kg IV infusion.

Surgical & Procedural Management

Lung transplantation for end-stage fibrotic lung disease (Stage IV). Pacemaker/ICD placement is critical for patients with cardiac sarcoidosis presenting with conduction blocks or arrhythmias.

Recommended Lifestyle Changes

• Avoid excessive calcium and Vitamin D supplements to prevent hypercalcemia and kidney stones.
• Avoid excessive sun exposure (UV light stimulates dermal synthesis of Vitamin D, exacerbating hypercalcemia).
• Smoking cessation is critical to preserve remaining lung function.

Patient Counseling & Advice

Inform patients that the disease often goes away on its own without treatment. Annual eye exams by an ophthalmologist are mandatory to catch asymptomatic uveitis before it causes blindness. Report any new palpitations or fainting spells immediately, as they may indicate cardiac involvement.

Follow-Up & Monitoring Schedule

Pulmonary function tests (Spirometry and DLCO) and Chest X-ray every 3-6 months. Annual ECG to screen for heart block. Routine basic metabolic panel to monitor serum calcium and creatinine.

Preventive Strategies

No known preventive measures as the etiology remains unknown.

Generally good; up to 60-70% achieve spontaneous remission within 2-5 years. However, 10-20% suffer permanent lung damage. Mortality is 1-5%, primarily from advanced pulmonary fibrosis, cardiac arrhythmias, or neurologic involvement.