[Middle lobe syndrome--incidence and relationship to atypical mycobacterial pulmonary disease]

We evaluated the incidence of middle lobe syndrome in the Haibara area, and its relationship to atypical mycobacterial infection. Of the 30,588 persons who underwent annual mini-chest roentgenography in 1992 or 1993 or both, 51 (0.17%) had middle lobe syndrome, diagnosed from posteroanterior and lateral chest X-ray films. The incidence was significantly higher in persons over 50 years old than in persons under 50 years old (0.26% vs 0.02%: p < 0.001), and was higher in femals than in males (0.20% vs 0.11%: p = 0.527). Of 16 patients examined by bronchoscopy and computed tomography, 7 showed evidence of cylindrical bronchiectasis, and four had mycobacterium avium complex pulmonary disease presenting as middle lobe syndrome. All four were women who were 51 years of age or older and none had predisposing pulmonary disorders. Computed tomography showed multiple nodular shadows with or without bronchiectasis located in the middle lobe or the lingula. Cavitary lesions were not seen. These results indicate that middle lobe syndrome is not rare, and that infection with mycobacterium avium complex should be considered when multiple nodular shadows are seen in the middle lobe or the lingula.