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Sarcoidosis

Summary

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  • Multisystem granulomatous disorder of unknown aetiology
  • Characterised by non-caseating granulomas in affected organs
  • Primarily affects lungs and lymph nodes; can involve any organ system

Pathophysiology

  • Exact cause unknown; likely involves abnormal immune response to environmental triggers
  • Formation of non-caseating granulomas in affected tissues
  • Granulomas consist of epithelioid cells, multinucleated giant cells, and lymphocytes
  • Activated T-cells and macrophages play a key role in granuloma formation

Demographics

  • Peak incidence: 20-40 years of age
  • More common in women
  • Higher prevalence in African Americans and Northern Europeans
  • Familial clustering suggests genetic predisposition

Diagnosis

  • No single diagnostic test; based on clinical presentation, imaging, and histopathology
  • Exclusion of other granulomatous diseases (e.g., tuberculosis, fungal infections)
  • Elevated serum angiotensin-converting enzyme (ACE) levels in 60-80% of cases
  • Bronchoalveolar lavage: increased CD4/CD8 T-cell ratio
  • Tissue biopsy: non-caseating granulomas

Imaging

  • Chest radiography:

    • Bilateral hilar lymphadenopathy (most common finding)
    • Reticular opacities and nodules in lung parenchyma
    • Staging system based on chest X-ray findings (Scadding stages 0-IV)

  • High-resolution CT (HRCT):

    • Perilymphatic nodules
    • Ground-glass opacities
    • Fibrotic changes in advanced stages
    • Mediastinal and hilar lymphadenopathy

  • 18F-FDG PET/CT:

    • Useful for assessing disease activity and extrapulmonary involvement
    • Increased FDG uptake in active granulomatous lesions

  • Cardiac MRI:

    • Evaluation of cardiac sarcoidosis
    • Late gadolinium enhancement in affected myocardium

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  • A 50-year-old patient presented with vague neurological symptoms including cognitive impairment.
  • MRI showed a diffuse leukoencephalopathy with striking perivascular enhancement.
  • Biopsy revealed granulomatous inflammation compatible with neurosarcoidosis.

Treatment

  • Many patients require no treatment; spontaneous remission in up to 60% of cases

  • Corticosteroids: first-line therapy for symptomatic or progressive disease

    • Prednisone: initial dose 20-40 mg/day, tapered over 6-12 months

  • Second-line agents for refractory cases or steroid-sparing:

    • Methotrexate
    • Azathioprine
    • Hydroxychloroquine
    • Anti-TNF-α agents (e.g., infliximab)

  • Organ-specific treatments:

    • Cardiac sarcoidosis: antiarrhythmic drugs, implantable cardioverter-defibrillators
    • Ocular sarcoidosis: topical corticosteroids, immunosuppressants

  • Regular follow-up and monitoring of organ function and treatment response

Differential diagnosis

Differential diagnosis Differentiating feature
Lymphoma (primary CNS or systemic) Periventricular mass lesions with ring or homogeneous enhancement; marked diffusion restriction on DWI; no perivascular predilection
Tuberculosis Predominantly basilar leptomeningeal enhancement; ring-enhancing tuberculomas with central restricted diffusion; calcifications on CT
IgG4-related disease Nodular dural/pachymeningeal thickening and enhancement; orbital pseudotumour; pituitary stalk and infundibular involvement
Leptomeningeal carcinomatosis Diffuse nodular leptomeningeal enhancement without perivascular predominance; may involve cranial nerves diffusely
Multiple sclerosis Periventricular ovoid white matter lesions (Dawson's fingers); calloso-septal interface lesions; no leptomeningeal or cranial nerve enhancement
Langerhans cell histiocytosis Hypothalamic and pituitary stalk thickening; lytic skull lesions on CT; absence of perivascular leptomeningeal enhancement
Neurosyphilis Meningeal enhancement and vessel wall involvement on high-resolution MRI; can appear identical to neurosarcoidosis
Granulomatosis with polyangiitis (GPA) Skull base destruction and paranasal sinus involvement on CT; orbital soft tissue infiltration; dural-based enhancing masses