A young child with cough and fever
Chest Xray shows subsgemetnal atelectasis with transverse fissure thickening with hilar lymphadenopathy and mottled infrahilar reticulation possibly lymphangitis – together called primary complex disease(Ranke’s complex)
Teaching points by Dr MGK Murthy
- Tubercle bacilli as little as 1-3 can reach the respiratory tree of the child invariably from cavitating adult contact usually at home or school/daycare environment as the bacilli are really killed by ultraviolet light outside
· The bacilli can be expelled by the cilia to be swallowed and destroyed by the stomach acid or can reach alveoli to be inhibited/killed by the macrophages.
· If they are virulent , multiply and burst macropahges to spread forming tubercle (aggregation of macrophages, epitheloid cells and lymphocytes)
· Immune response at this stage(3-8 wks) is delayed hypersensitivity and tuberculin test is positive
· Bacilli escape from edge, multiply and reach lymphnodes .
· All the 3 components alveolar site (ghon’s focus), lymphangitis and infected mediastinal lymphnode form Primary complex mediated by cell mediated immunity (Ranke’scomplex)
· Chest Xray/CT is + by 4-8 wks after the exposure
· Can involve any part of the lung but middle lobe is least involved
· 95%do not suffer from disease and X ray shows only fibrosis, calcification or completely normal
· Radiological hallmark is lymphadenopathy
· Because of peculiarity of lymphatics, left parenchymal lesion produces bilateral and right parenchymal shows only right hilar lymphnodes possibly along with transverse fissure fluid
· When the lesion erodes the lymphnode and spreads along the bronchus it will become progressive primary TB
· If TB infection occurs 1 year or later after the original infection, referred to as post primary from usually because of reactivation
· Post primary prefers colonization in upper lobes specially apical and posterior segments
· Child to child transmission is rare because of lack of tussive outburst
· Miliary and Meningeal forms develop in 1st 3months after primary complex
· Pleural and peritoneal forms take 3-7 months to manifest
· One variety called congenital TB is extremely rare possibly because of hypoxic intrauterine environment does not promote TB bacilli growth.
· But when occurs ,usually via transplacental spread-----primary complex is in liver –periportal LNs –other organs and lungs can remain latent for 2-4 wks after birth and when Xray is +, it shows miliary form
· Even more rarely can occur by foetus swallowing bacilli in genital TB