Aetiology
Pathophysiology
The characteristic finding is the presence of non-caseating granulomas with multi-nucleated giant cells in the centre. CD4 lymphocytes are spread out through the granuloma, and CD8 cells cluster around the periphery. The CD4 lymphocyte and associated cytokines, such as interferon gamma, interleukin (IL)-2, and IL-12, promote and maintain the granulomas.
Alveolar macrophages behave as versatile secretory cells that release a variety of cytokines, including tumour necrosis factor (TNF)-alpha, IL-12, IL-15, and growth factors. The immunological pattern of cells in the sarcoid infiltrate suggests that sarcoid granulomas are formed in response to a persistent and probably poorly degradable antigenic stimulus that induces a local T-cell-mediated immune response with an oligoclonal pattern. As a consequence of their chronic stimulation, macrophages release mediators of inflammation locally, leading to accumulation of T-helper type 1 cells at sites of ongoing inflammation and contributing to the development of the granuloma structure.
Classification
Commonly used classification according to organ/system involvement
Systemic sarcoidosis: multi-system involvement, sometimes with chronic fatigue.
Pulmonary sarcoidosis: >90% of patients; further classified into stages I, II, III, and IV (Siltzbach classification); cough; dyspnoea that can be progressive based on cardiopulmonary involvement.
Cutaneous sarcoidosis: plaques; lupus pernio.
Ocular sarcoidosis: uveitis most common subtype; anterior uveitis most common in white people; posterior uveitis and panuveitis more prevalent among black people.[2]
Cardiac sarcoidosis: clinically overt in 5% to 10% of patients but may occur in 20% to 50% of cases.[3][4] Arrhythmias; various types of heart block; congestive heart failure; cardiomyopathy later in course; if pulmonary arterial hypertension occurs, can be debilitating; sudden cardiac death.
Neurosarcoidosis: <15% of patients; cranial nerve palsies; headaches; seizures.[5]
Renal sarcoidosis: clinically significant renal involvement is rare; most commonly due to disordered calcium metabolism; granulomatous interstitial nephritis; glomerulonephritis.[6]
Siltzbach classification system[7]
Classification relates to granulomas present in the lymph nodes and the lungs and is determined using chest x-ray. The five stages of pulmonary sarcoidosis are:
Stage 0 (no pulmonary sarcoidosis): no sign of granulomas in the lungs or lymph nodes
Stage 1 (lymphadenopathy): granulomas present in the lymph nodes only
Stage 2 (lymphadenopathy and pulmonary infiltrates): granulomas present in both the lymph nodes and the lungs
Stage 3 (pulmonary infiltrates): granulomas present in the lungs only
Stage 4 (pulmonary fibrosis): scarring of the lung tissue and permanent damage.
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