title: Lessons from Mycobacterium avium complex-associated pneumonitis: a case report.
abstract: BACKGROUND
  Mycobacterium avium complex (MAC) is an increasingly recognized cause of pulmonary disease in immunocompetent individuals. An acute form of MAC lung disease, MAC-associated pneumonitis, has generally been associated with the use of hot tubs. There is controversy in the literature about whether MAC-associated pneumonitis is a classic hypersensitivity pneumonitis or is a direct manifestation of mycobacterial infection.
  
  
  METHODS
  We report the second case in the literature of MAC-associated pneumonitis not related to the use of hot tubs. The source of MAC in a 52-year-old immunocompetent patient was an intrapulmonary cyst containing numerous acid-fast bacilli. The patient developed disseminated miliary nodules throughout both lung fields. Histological examination of resected lung tissue revealed well-formed, acid-fast negative granulomas composed predominantly of CD4+ T-cells and CD68+ histiocytes. The granulomas were strongly positive for tumor necrosis factor-alpha, a pro-inflammatory cytokine.
  
  
  CONCLUSIONS
  The attempt to classify MAC-associated pneumonitis as either a classic hypersensitivity pneumonitis or a direct manifestation of mycobacterial infection is not particularly useful. Our case demonstrates that MAC-associated pneumonitis is characterized by a vigorous T-helper 1-like, pro-inflammatory, immune response to pulmonary mycobacterial infection. The immunopathology provides a rationale for clinical studies of anti-MAC therapy with the addition of anti-inflammatory agents (for example, corticosteroids) to hasten the resolution of infection and symptoms.
authors.affiliation: Department of Pathology, Division of Infectious Disease, University of Massachusetts Medical School, Worcester, MA, USA. zotav@ummhc.org
authors.forename: Victor
authors.initials: V
authors.lastname: Zota
authors.forename: Sheryn M
authors.initials: SM
authors.lastname: Angelis
authors.forename: Armando E
authors.initials: AE
authors.lastname: Fraire
authors.forename: Ciaran
authors.initials: C
authors.lastname: McNamee
authors.forename: Shasta
authors.initials: S
authors.lastname: Kielbasa
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Libraty