Pathology of TB and fungal infections Flashcards
Primary TB I pathogenesis
Previously unexposed person Exogenous organism (typically in distal parts of lower upper lobe, or upper lower lobe, close to the pleura) As sensitization develops, 1-1.5 cm area of gray-white inflammatory consolidation = Ghon focus --> most centres undergo caseous necrosis Tubercle bacilli drain to regional lymph nodes, which also often caseates
1st few weeks, lymphatic and hematogenous dissemination
Ghon complex –> fibrosis –> calcification
Seeding of other organs
May progress w/o interruption to progressive pulmonary primary TB
Ghon complex
combination of parnechymal + nodal involvement (caseates)
Progressive pulmonary primary TB
common in immunocompromised
inability to mount a CD4+ T-cell mediated immunologic response to contain primary lesion
may result in miliary TB and tuberculous meningitis
Secondary (Reactivation) TB I pathogenesis
Usually many decades after initial infection, when host defense is weakened
May also result from exogenous re-infection
Classically localized to the apex of one or two lobes
Cavitation occurs readily –> dissemination along airways
Erosion into airway –> release of bacilli-containing sputum
Variable amount of central caseation and peripheral fibrosis
Favourable cases: progressive fibrous encapsulation (leaves fibro-calcific scar)
Localized apical secondary pulmonary TB may heal with fibrosis, spontaneously or after therapy
Complications of secondary TB
Erosion into bronchi with cavitation BV erosion --> hemoptysis Miliary pulmonary disease Pleural effusion/tuberculous empyema Endobrachial/endotracheal/laryngeal TB Systemic miliary TB Isolated-organ TB, e.g. TB meningitis Lymphadenopathy, usually cervical region (scrofula) Death
Non-tuberculous mycobacterial species
Mycobacterium avium complex (MAC)
Mycobacterim kansii
Mycobacterium abcessus
Affects immunocompetent host
Non-tuberculous mycobaterial disease risks
COPD
CF
pneumoconioses
long Hx of smoking, alcoholism (mimicks TB, upper lobar cavitary disease)
MAC infection & Disease, Sx
Immunocompromised host
Disseminated disease with systemic Sx (fever, night sweats, weight loss)
Hepatosplenomegaly, lymphadenopathy
GI symptoms
Pulmonary involvement indistinguishable from TB
Tends to occur when CD4 instead, find foamy macrophages, “stuffed” with atypical mycobacteria
Multi-drug resistant TB (MDR-TB)
Resistant to two or more primary drugs
concern in HIV patients
Prognosis of TB
Favourable if localized to lung
Worsens with age, debilitated, immunocompromised, MDR-TB
Fungal infections in immunocompetent host - agents
Blastomyces dermatidis Histoplasma capsulatum Coccidiodes immitis Cryptococcus neoformans Cryptococcus gattii (BC)
organisms manifest as spores
Fungal infections in immunocompetent host - presentation
Pathological and clinical/radiological similarity to TB
Granulomatous inflammation + necrosis
Acute (primary) pulmonary infection
Chronic (incl. cavitary) pulmonary disease
Disseminated miliary disease
Solitary pulmonary nodule & Peri-hilar mass/lymphadenopathy resembling bronchogenic carcinoma radiologically
Differentiation from TB requires culture
Fungal infections in immunocompromised host - agents
Aspergillus
Candida
Mucor
Organisms manifest as fungal hyphae
Fungal infections in immunocompromised host - presentation
Necrotizing pneumonia
Propensity for BV invasion (angioinvasion)
Consequent tissue infarction
Systemic dissemination, esp. to the brain
Sarcoidosis
Disease of unknown etiology characterized by non-caseating/non-necrotizing granulomas, which can also be produced by mycobacterial & fungal infections
Diagnosis of exclusion - look for fungal/MB spherules
