Nontuberculous Mycobacterium Infections in Rheumatoid Arthritis Patients

Nontuberculous mycobacteria (NTM) are a large, diverse group of ubiquitous environmental organisms found in tap water, soil, dust, plants, animals, and food. NTM infection can cause various diseases, such as pulmonary disease (PD), which are most frequently observed in immunocompromised individuals. Diseases associated with NTM are particularly severe in those receiving tumor necrosis factor (TNF)-alpha (α) blockers, which predispose individuals to NTM infection. Experts generally agree that patients with active NTM disease should receive TNF-α blockers only if they are also receiving adequate therapy for NTM disease. On the other hand, the Japanese College of Rheumatology recommends that TNF-α blockers not be used in patients with active NTM infection, because NTM is resistant to most antimycobacterial drugs. Bronchiectasis is one of the most frequent manifestations of NTM infection, not only in NTM-PD patients, but also in rheumatoid arthritis (RA) patients. It is difficult to distinguish the bronchiectasis associated with NTM-PD from that with RA on chest radiography or high-resolution computed tomography (HRCT). Due to the ease of NTM contamination from the environment, the diagnosis of NTM-PD is extremely difficult. The most recent American Thoracic Society (ATS) and Infectious Disease Society of America (IDSA) guidelines recommend diagnosing NTM-PD via a combination of clinical, radiographic, bacteriologic (two positive sputum cultures, or one positive bronchoalveolar lavage (BAL) culture or transbronchial biopsy), and histological criteria. In NTM-PD patients receiving TNF-α blockers, Mycobacterium avium was the most common etiologic organism, accounting for half of all NTM isolates (Winthrop et al., 2009). Recently, Kitada et al. (2008) established an enzyme immunoassay (EIA) for the serological diagnosis of M. avium-complex (MAC)PD by examining the level of serum IgA antibody to the glycopeptidolipid (GPL) core, which is a MAC-specific antigen. Unlike bronchoscopy and sputum culture examinations, EIA kits are less invasive and provide more rapid diagnosis of MAC-PD. In this chapter, we discuss the characteristics of NTM, relationship between NTM infections and RA patients, particularly those receiving TNF-α blockers, and diagnosis of MAC-PD with RA patients using the recently developed EIA kit.