Welcome to Cross-Canada Paediatric - Respiratory Residency Rounds
Page 8/Case04/01


1) Background: Bacteriology, identification, transmission
2) Clinical Features
3) ATS Criteria for Diagnosis
4) Treatment: Medical, surgical
5) Adjunctive therapy
6) Prognosis and outcomes

– Non-motile, non-spore forming, slender, pleomorphic bacteria with complex cell walls
– Ubiquitous bacterium: Found in soil, water, house dust
– > 50 mycobacterial species, about one half are pathogenic. Runyon classification; pigment and speed of growth
– Most commonly encountered organisms: M. avium, M intracellulare, M. scrofulaceum

– Ziehl-Neilsen stain methylene blue – sensitivity < 50% on sputum and tissue samples in children
– Fluorochrome stain, auramine rhodamine
– PCR technique (Haas et al, 1998)

Culture Identification and caveats
– ~ 10,000 AFB/ml of specimen to be seen on a smear
– Susceptible to being killed by alkali agents
– Growth of colonies may take 10 days (rapid growing) up to 6 wks (slow growing)
– Rapid growth of MAC may obscure MTB growth
– Drug susceptibility reports should be interpreted with caution

Mode of Transmission
– Probable aerosol transmission, not human-to-human
– Mechanism of infection: Use complex glycopeptidolipid cell wall to downregulate macrophage responses and infect cells, then release of cytokines that recruit and stimulate lymphocytes from innate and acquired immune system. Defective cytokine production implicated (IL-12), TNF
– Low virulence unless immunocompromised (mycobacterium avium complex reported in men with underlying pulmonary disease, some older women without underlying disease and disseminated infections in those with HIV)

Clinical Features and Presentation of atypical mycobacterium pulmonary disease
– Highly variable, lung involvement usually adolescents and adults
– Cervical lymphadenitis (most common presentation in children) (McCabe et al. JAMA 1984;Gilbert Am Rev Respir Dis 1972)
– Pneumonia
– Mediastinal lymphadenopathy
– Significant extrinsic bronchial compression
– Endobronchitis
– Invasive disease (more likely if immunocompromised, i.e. HIV)
– Can resemble human tuberculosis**

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