Sarcoidosis: Unknown Etiology and Genetic Predisposition Provides Therapeutic Challenges

Sarcoidosis is an idiopathic multisystem disorder characterized by noncaseating epithelioid granulomas predominately affecting lungs and lymph nodes, but with potential to affect any organ system. Sarcoidosis shares similarities in development to other infectious granulomatous diseases, such as berylliosis and tuberculosis; however, its elusive etiology and non-distinctive histology have provided many diagnostic challenges. Evidence of a transferrable antigen combined with a high incidence rate in the lungs has focused efforts primarily on antigens with airborne transmissibility. While Mycobacterium tuberculosis and Propionibacterium acnes have provided strong associations to implicate each as a contributor to sarcoidosis pathogenesis, detection challenges remain and consensus of a definitive antigen is lacking. Uncovering common polymorphisms has added another layer to the pathophysiology of sarcoidosis. Polymorphisms involving BTNL2, NODS, Notch and Anxa11, as well as certain HLA alleles, such as DRB1*0301 and DRB1*1101 may confer predisposition or resistance to sarcoidosis. Additionally, polymorphisms such as BTNL2 rs2076530 and Anxa11 rs1049550 show efficacy in increasing susceptibility or have no effect in certain ethnic groups. These polymorphisms also show familial linkages and may provide markers for disease severity. Without definitive diagnostic criteria, sarcoidosis remains a multistep diagnosis of exclusion. Therapeutics has improved clinical management of sarcoidosis while providing an avenue to further elucidate a possible antigen. While corticosteroids are often used as a first line of defense, unacceptable side effects may occur, leading to the implementation of alternative therapeutics. Alternatively, Disease Modifying Anti-Rheumatic Drugs, antimalarial drugs, Tumor Necrosis Factor Alpha (TNF-α) antagonists and antimicrobial drugs have recently been implemented with beneficial results. In this review we discuss potential causative antigens, diagnostic challenges associated with sarcoidosis and review current therapeutics.