Sarcoidosis is a systemic disease of unknown cause characterized by the formation of immune granulomas which most often involve the lung and the lymphatic system. Sarcoidosis may encompass numerous different clinical presentations. Typical presentations often prompt a rapid diagnosis while in 25 to 50% of cases, diverse and less typical presentations may lead to delayed diagnosis. The mediastinopulmonary sphere is involved in 85 to 95% of cases, associated with extrapulmonary localizations in half of cases while extrapulmonary localizations without lung involvement may be seen in 5 to 15% of cases. Bilateral hilar lymphadenopathy is the most typical sign at chest radiography. Computed tomography (CT) is essential face for atypical manifestations of the disease to avoid confusion with differential diagnoses and, sometimes, comorbidities. CT typically evidences diffuse pulmonary perilymphatic micronodules, with a perilobular and fissural distribution and upper and posterior predominance, even when an atypical CT pattern is predominant. CT allows deciphering pulmonary lesions in cases of pulmonary fibrosis, pulmonary hypertension, and airflow limitation. Pulmonary function tests generally correlate with the overall disease process. Forced vital capacity is the simplest and most accurate parameter to reflect the impact of pulmonary sarcoidosis. Cardiopulmonary exercise testing helps in understanding the mechanism behind dyspnea of uncertain origin. Endoscopic transbronchial needle aspiration is an extra tool to support diagnosis in addition to more classical biopsy means. Bronchoalveolar lavage (BAL) may be used for individual patients while it is not really decisive for the diagnosis of sarcoidosis for most patients. Diagnosis relies on compatible clinical and radiological presentation, evidence of noncaseating granulomas and exclusion of other diseases with a similar presentation or histology. The probability of diagnosis at presentation is variable from case to case and may often be reinforced with time. Some investigations are mandatory at diagnosis to assess organ involvement and disease activity. However, there are important variations in diagnostic work-up due to diverse expressions of sarcoidosis and differences in clinical practices among physicians.
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