Pulmonary Tuberculosis. Evolution and Clinical picture. Global burden of TB . In 1993 WHO declared TB a global emergency . It is estimated that 9 million new cases of TB occurred /year and 3 million TB deaths/year . Tuberculosis poses a major problem for developing countries .
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Evolution and Clinical picture
• Appears against the protein part of the bacillus.
• reflected pathologically as caseous necrosis by the 2nd wk.
•Early in prim infection bacillemia occurs through lymph-hematogenous spread with seeding of bacilli to all parts of the lungs and also other body organs.
•These dormant foci are reactivated later on with marked potential variability according to local and general resistance.
•Regression occurs when:
Low virulence of bacilli
High host resistance
•Resolves & disappear completely by absorption
•Healing by fibrosis, calcification & even ossification
•Some bacilli may be imprisoned alive and become active again when resistance decreases
• Occurs when
high virulence or dose of bacilli
low host resistance
bronchial vein Rt side of Ht lungs
pulmonary vein Lt side of Ht allover the body
pulmonary artery one lung dissemination
(1)Good fate (regressive primary)
as lung component
(2)Bad fate (progressive)
compression Þ brassy cough
partial obstruction Þ emphysema
complete obstruction Þ collapse
erosion Þ aspiration
(2)Rupture in blood vessel Þ hematogenous spread
• brief febrile illness at the time of tuberculin conversion that is indistinguishable from the many febrile illnesses of childhood. Most children are symptom-free and are discovered only when they are investigated as contacts of an adult case,
• may occur in elderly people who have lost their tuberculin sensitivity.
• In most cases there are no detectable physical signs.
• the child may be unwell with loss of appetite, fretfulness and failure to gain weight.
• Sputum production is rare in children.
• Auscultation of the chest occasionally crepitations may be heard over an extensive primary focus.
• More obvious physical signs may be present if there is segmental or lobar exudation or collapse.
- Post. tuberculinreaction.
• This term is not used now
• It describes dense homogenous shadow in lung of children with tuberculosis.
•This radiological appearance is due to
- hypersensitivity reaction to tubercle protein
- tuberculous pneumonitis (rarely caseating)
- collapse by
pressing lymph node
pouring of caseous material
caseous bronchitis and stenosis
- Allergic pleural effusion.
• Infection occurring after sometime from the primary infection.
• Tissue reaction is different from that in prim reaction because the ground has been changed by acquired immunity & hypersensitivity.
• Unlike prime disease, postprim bronchogenic TB is characterised by increased local destruction caseation and cavity formation while lymph nodes enlarge rarely and lately (if suppressed immunity).
• This is because enhanced phagocytic activity prevents spread to lymph nodes aiming at localising infection and destroying bacilli.
A disease caused by dissemination of tubercle bacilli via blood to involve more than one organ not related to each other except by blood stream.
Seeding of bacilli into vessel walls may cause a caseous vasculitis of the intima , with subsequent discharge of bacilli into the blood stream leading to miliary spread. Usually solitary, caseating and liquefying but can later heal by endothelial covering. Can occur in large veins & thoracic duct but less commonly in arterial system.
Large no of bacilli + poor resistance
small no of bacilli + good resistance
takes months or years to develop
• Characterised by millet seed sized foci uniformly distributed throughout the lung or other involved organs.
• A typical tubercle structure is not commonly seen in acute form unlike the chronic.
• The more acute the less pronounced the caseous reaction.
Acute or classical miliary tuberculosis
Pathologically characterized by :
• tendency to fibrosis & calcification.
• caseation plays a minor role
• restriction of spread to certain areas (bronchi are rarely involved)
• presence of extra pulmonary lesions.
• symmetrical distribution
• uniformity of size fo the lesions
• ± calcification or bilateral pleural effusion.**
• General toxemia
• Lack of local signs & symptoms (cough, expect, hemoptysis are not usual)
(1)Chronic miliary dissemination
sharply defined foci with typical tubercle structure connected with fibrotic strands
groups of foci are seen at the margin of one lobe beneath & implicating the pleura
(3)Disseminated emphysematous type
characterised by fibrosis alveolar dilatation emphysema & bullous formation (bullae alternating with fibrosing military nodules)
(4)Punched out cavities
•thin walled stamped out cavities
•no sputum as necrotic material is absorbed by blood rather than expectorated
•either heal or persist as thin walled spaces over years.
•differ from cavities of bronchogenic TB that show thick fibrosed walled & caseation.
•large apical foci with caseating or calcified centers surrounded by fibrosed lung and covered by fibrosed pleura (fibrosa densa)
1-bilateral hilar (& other mediastinal glands??)
2-bone & joint
5-serous membranes & meninges
• virulence of bacilli
• hypersensivity of the host
• local O2, CO2 & blood flow
1- apical reaction with fibrosis with or without calcification
living bacilli will be left in this focus & may cause bacillemia later on.
2- chronic fibrocaseous TB
The Rt lung is more affected (usually subapically i.e. post. Seg. Of UL & apex of LL)
Lower lobe TB is common in:
Diabetes Negroes pregnancy
In general, examination of the chest contributes relatively little to the diagnosis or assessment of postprimary tuberculosis. Sputum examination and chest radiography are much more important. However, it is essential to conduct a general examination of the patient as there may be additional tuberculous lesions outside the chest.
The following characteristics of a chest radiograph favour the diagnosis of tuberculosis :
1.opacities mainly in the upper zone(s);
2.patchy or nodular opacities;
3.presence of a cavity or cavities;
4.presence of calcification;
5.bilateral opacities especially if in upper zones;
6.opacities that persist after several weeks (and thus are less likely due to acute pneumonia).
Lesions more extensive than moderately advanced.
4.Tuberculosis of other organs.
5.Chronic obstructive airways disease.
9.Carcinoma of the bronchus.
10.Adult respiratory distress syndrome.