Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis. Despite the availability of novel therapeutic approaches, TB is considered as one of the leading causes of death due to
infectious diseases worldwide. Alveolar macrophages are the first line of defense against M.
tuberculosis; they ingest and sequester the bacilli within granulomatous structures. Control and resolution of the
infection requires activated T lymphocytes as well as Th1
cytokines. There are two forms of TB: active TB and latent TB. Latent TB is a state in which M.
tuberculosis survives in the body without causing overt signs and symptoms. People with latent TB are noncontagious. However, M.
tuberculosis can become active in the body, multiply, and cause overt TB.
Sarcoidosis, on the other hand, is an
autoimmune disease of unknown etiology which can affect multiple systems of the body. Nonspecific constitutional symptoms, such as
fever,
fatigue, malaise, and
weight loss, are present in approximately one-third of patients. Chest X-ray usually shows hilar and mediastinal
lymphadenopathy. Although the lungs are the most common sites of
inflammation,
sarcoidosis can also involve other organs, such as the eyes (intraocular and adnexal), skin, lymph nodes, salivary glands, heart, spleen, liver, and the nervous system. Recent investigations have provided further insights into the genetic basis of
sarcoidosis and the way genotype determines the clinical presentation and phenotype of patients. Histopathologic features are usually insufficient for diagnosis of
sarcoidosis. Diagnosis of
sarcoidosis in endemic areas for TB can become a great challenge. Both TB and
sarcoidosis are granulomatous diseases; TB is characterized by caseating
granulomas, whereas
sarcoidosis is characterized by noncaseating
granulomas. New cases of
sarcoidosis are increasingly being diagnosed in areas endemic for TB due to increased orientation of physicians and availability of diagnostic modalities. However, it is often difficult to differentiate
sarcoidosis from TB, especially when caseous
necrosis is not seen and
acid-fast staining is negative in the biopsy specimen of patient with TB. Granulomatous
inflammation in
sarcoidosis is believed to be caused by the presence of a persistent poorly degradable unknown
antigen in combination with a nonresolving host response. M.
tuberculosis has been extensively studied as a possible cause of
sarcoidosis. Results suggest that
granulomas form in the lungs as a result of the immune response to inhaled M.
tuberculosis and serve as the central site of host-pathogen interaction during M.
tuberculosis infection. M.
tuberculosis DNA detection in
sarcoidosis samples by traditional polymerase chain reaction (PCR) has been used for the pathological study of
sarcoidosis; however, it is likely that real time quantitative PCR analysis of specific mRNAs and
microRNAs will be necessary as a sensitive, precise, and rapid diagnostic test for detecting trace of TB in
Sarcoidosis. In conclusion, diagnosis of
sarcoidosis in areas with a high burden of TB poses a significant challenge. Improved diagnostic tests including genetic tests can improve our knowledge and help in distinguishing these two diseases.