Respiratory system

Dr.Dhaher JS Al-habbo FRCP London UK Assistant Professor in Medicine DEPARTMENT OF MEDICINE
Tuberculosis

Tuberculosis (TB)

Tuberculosis (TB) is caused by infection with Mycobacterium tuberculosis (MTB), which is part of a complex of organisms including M. bovis (reservoir cattle) and M. africanum (reservoir human). With1.5 million deaths attributable to TB. One-third of the world's population has latent TB. The majority of cases occur in the world's poorest nations. The resurgence of TB has been largely driven in Africa by HIV disease, and in the former Soviet Union and Baltic states by lack of appropriate health care exacerbated by social and political upheaval.

Tuberculosis (TB)

Tuberculosis (TB) is caused by infection with Mycobacterium tuberculosis (MTB), M. tuberculosis is spread by the inhalation of aerosolised droplet nuclei from other infected patients.

Once inhaled, the organisms lodge in the alveoli and initiate the recruitment of macrophages and lymphocytes. Macrophages undergo transformation into epithelioid and Langhans cells which aggregate with the lymphocytes to form the classical tuberculous granuloma . M. bovis infection arises from drinking non-sterilised milk from infected cows.

Tuberculosis (TB)

Numerous granulomas aggregate to form a primary lesion or 'Ghon focus' ,which is characteristically situated in the periphery of the lung. Also spread of organisms to the hilar lymph nodes is followed by 'Ghon focus reaction; Combination of a primary lesion and regional lymph nodes is referred to as the 'primary complex of Ranke'. Reparative processes encase the primary complex in a fibrous capsule limiting the spread of bacilli: so-called latent TB. If no further complications ensue, this lesion eventually calcifies and is clearly seen on a chest X-ray

Ghon focus

Primary Complex of Ranke

Factors increasing the risk of TB

Patient-related Age (children > young adults < elderly) ,Close contacts of patients with smear-positive pulmonary TB ,Overcrowding, Chest radiographic evidence of self-healed TB , Smoking: cigarettes Primary infection < 1 year previously

Factors increasing the risk of TBAssociated diseases

Immunosuppression: HIV, anti-TNF therapy, high-dose corticosteroids, cytotoxic agents Malignancy (especially lymphoma and leukaemia) Type 1 diabetes mellitus ,Chronic renal failure ,Silicosis Gastrectomy, jejuno-ileal bypass, cancer of the pancreas, malabsorption. Deficiency of vitamin D or A Recent measles: increases risk of child contracting TB

Timetable of TB

Time from infection
Primary complex, positive tuberculin skin test
3-8 weeks
Meningeal, miliary and pleural disease
3-6 months
Gastrointestinal, bone and joint, and lymph node disease
Up to 3 years
Renal tract disease
Around 8 years
Post-primary disease due to reactivation or reinfection
From 3 years onwards

Features of primary TB infection(4-8weeks)

Influenza-like illness. Skin-test conversion. Primary complex. Hypersensitivity . Erythema nodosum. Phlyctenular conjunctivitis . Dactylitis

Primary TB

Primary TB refers to the infection of a previously uninfected (tuberculin-negative) individual. A few patients develop a self-limiting febrile illness but clinical disease only occurs if there is a hypersensitivity reaction or progressive infection . Progressive primary disease may appear during the course of the initial illness or after a latent period of weeks or months.

Miliary TB

Blood-borne dissemination gives rise to miliary TB, which may present acutely but more frequently is characterised by 2-3 weeks of fever, night sweats, anorexia, weight loss and a dry cough. Hepatosplenomegaly may develop and the presence of a headache may indicate coexistent tuberculous meningitis. Auscultation of the chest is frequently normal, although with more advanced disease widespread crackles are evident. Fundoscopy may show choroidal tubercles. The classical appearances on chest X-ray are of fine 1-2 mm lesions ('millet seed') distributed throughout the lung fields, although occasionally the appearances are coarser. Anaemia and leucopenia reflect bone marrow involvement. 'Cryptic' miliary TB is an unusual presentation sometimes seen in old age

Post-primary pulmonary TB

Cryptic M. TB Age over 60 years Intermittent low-grade pyrexia of unknown origin Unexplained weight loss, general debility (hepatosplenomegaly in 25-50%) Normal chest X-ray Blood dyscrasias; leukaemoid reaction, pancytopenia Negative tuberculin skin test Confirmation by biopsy (granulomas and/or acid-fast bacilli demonstrated) of liver or bone marrow

Post-primary pulmonary TB

Clinical presentations of pulmonary TB Chronic cough, often with haemoptysis Pyrexia of unknown origin Unresolved pneumonia Exudative pleural effusion Asymptomatic (diagnosis on chest X-ray) Weight loss, general debility Spontaneous pneumothorax

Post-primary pulmonary TB

Post-primary disease refers to exogenous ('new' infection) or endogenous (reactivation of a dormant primary lesion) infection in a person who has been sensitised by earlier exposure. It is most frequently pulmonary and characteristically occurs in the apex of an upper lobe where the oxygen tension favours survival of the strictly aerobic organism. The onset is usually insidious, developing slowly over several weeks. Systemic symptoms include fever, night sweats, malaise, and loss of appetite and weight, and are accompanied by progressive pulmonary symptoms . Very occasionally, this form of TB may present with one of the complications of TB.

Post-primary pulmonary TB

Radiological changes include ill-defined opacification in one or both of the upper lobes, and as progression occurs, consolidation, collapse and cavitation develop to varying degrees . It is often difficult to distinguish active from quiescent disease on radiological criteria alone, but the presence of a miliary pattern or cavitation favours active disease. In extensive disease, collapse may be marked and result in significant displacement of the trachea and mediastinum. Occasionally, a caseous lymph node may drain into an adjoining bronchus resulting in tuberculous pneumonia.

Clinical features: extrapulmonary disease

Pulmonary Massive haemoptysis Cor pulmonale Fibrosis/emphysema Atypical mycobacterial infection Aspergilloma Lung/pleural calcification Obstructive airways disease Bronchiectasis Bronchopleural fistula

Clinical features: extrapulmonary disease

Non-pulmonary Empyema necessitans Laryngitis Enteritis(From swallowed sputum). Anorectal disease(From swallowed sputum). Amyloidosis Poncet's polyarthritis

TB Gastrointestinal disease

Upper gastrointestinal tract involvement is rare and is usually an unexpected histological finding in an endoscopic or laparotomy specimen. Ileocaecal disease accounts for approximately half of abdominal TB cases. Fever, night sweats, anorexia and weight loss are usually prominent and a right iliac fossa mass may be palpable. Up to 30% of cases present with an acute abdomen. Ultrasound or CT may reveal thickened bowel wall, abdominal lymphadenopathy, mesenteric thickening or ascites.

TB Gastrointestinal disease . Pericardial effusion and Constrictive pericarditis. TB of the Central nervous system disease . TB of Bone and Join Disease. TB of Genitourinary disease

Contrast enhanced abdominal CT of a 21 year-old female patient demonstratesmultiple mesenteric lymphadenopathy forming a conglomerate mass (arrows) with 6 cm in major axis. Most enlarged nodes have central hypoenhancing areas due to necrosis.

Diagnosis of Tuberculosis

Specimens required: Sputum* (induced with nebulised hypertonic saline if not expectorating) At least 2 but preferably 3, including an early morning sample Bronchoscopy with washings or BAL Gastric washing* (mainly used for children) At least 2 but preferably 3, including an early morning sample Extrapulmonary Fluid examination (cerebrospinal, ascitic, pleural, pericardial, joint): yield classically very low Tissue biopsy (from affected site); also bone marrow/liver may be diagnostic in patients with disseminated disease


Diagnostic Tests

TB-Diagnostic tests

The presence of an otherwise unexplained cough for more than 2-3 weeks, particularly in an area where TB is highly prevalent, or typical chest X-ray changes should prompt further investigation . Direct microscopy of sputum is the most important first step. The probability of detecting acid-fast bacilli is proportional to the bacillary burden in the sputum (typically positive when 5000-10 000 organisms are present).

TB-Diagnostic tests

By virtue of their substantial lipid-rich wall, tuberculous bacilli are difficult to stain. The most effective techniques are the Ziehl-Neelsen and rhodamine-auramine stains. The latter causes the tuberculous bacilli to fluoresce against a dark background and is easier to use when numerous specimens need to be examined; However, it is more complex and expensive, limiting applicability in resource-poor regions.

TB-Diagnostic tests

A positive smear is sufficient for the presumptive diagnosis of TB but definitive diagnosis requires culture. Smear-negative sputum should also be cultured, as only 10-100 viable organisms are required for sputum to be culture-positive. A diagnosis of smear-negative TB may be made in advance of culture if the chest X-ray appearances are typical of TB and there is no response to a broad-spectrum antibiotic.

TB-Diagnostic tests

TB-Diagnostic tests
New strategies for the rapid confirmation of TB at low cost are being developed; These include the nucleic acid amplification test (NAT), designed to amplify nucleic acid regions specific to MTB such as IS6110, and the MPB64 skin patch test, in which immunogenic antigen detects active but not latent TB, and has the potential to provide a simple, non-invasive test which does not require a laboratory or highly skilled personnel.

TB-Diagnostic tests

Drug sensitivity testing is particularly important in those with a previous history of TB, treatment failure or chronic disease, those who are resident in or have visited an area of high prevalence of resistance, or those who are HIV-positive. The detection of rifampicin resistance, using molecular tools to test for the presence of the rpo gene currently associated with around 95% of rifampicin-resistant cases, is important as the drug forms the cornerstone of 6-month chemotherapy..

TB-Diagnostic tests

If a cluster of cases suggests a common source, confirmation may be sought by fingerprinting of isolates with restriction-fragment length polymorphism (RFLP) or DNA amplification. The diagnosis of extrapulmonary TB can be more challenging. There are generally fewer organisms (particularly in meningeal or pleural fluid), so culture or histopathological examination of tissue is more important. In the presence of HIV, however, examination of sputum may still be useful, as subclinical pulmonary disease is common

Skin testing in TB: Tests using purified protein derivative (PPD)

Heaf test Read at 3-7 days Multipuncture method Grade 1: 4-6 papules Grade 2: Confluent papules forming ring Grade 3: Central induration Grade 4: > 10 mm induration Mantoux test Read at 2-4 days Using 10 tuberculin units Positive when induration 5-14 mm (equivalent to Heaf grade 2) and > 15 mm (Heaf grade 3-4)

Skin

False negatives Severe TB (25% of cases negative) Newborn and elderly HIV (if CD4 count < 200 cells/mL) Malnutrition Recent infection (e.g. measles) or immunisation Immunosuppressive drugs Malignancy Sarcoidosis
Skin testing in TB

Skin testing in TB

Tuberculin skin testing may be associated with false-positive reactions in those who have had a BCG vaccination and in areas where exposure to non-tuberculous mycobacteria is high. These limitations may be overcome by employing interferon-gamma release assays (IGRAs).

Skin testing in TB

These tests measure the release of IFN-γ from sensitised T cells in response to antigens such as early secreted antigenic target (ESAT)-6 or culture filtrate protein (CFP)-10 that are encoded by genes specific to the MTB and are not shared with BCG or opportunistic mycobacteria. The greater specificity of these tests, combined with the logistical convenience of one blood test, as opposed to two visits for skin testing, suggests that IGRAs will replace the tuberculin skin test in low-incidence, high-income countries.

Managements and Chemotherapy

They are based on the principle of an initial intensive phase (which rapidly reduces the bacterial population), followed by a continuation phase to destroy any remaining bacteria. Treatment should be commenced immediately in any patient who is smear-positive, or who is smear-negative but with typical chest X-ray changes and no response to standard antibiotics.

Continuation phase

Initial phase*
Category of TB
4 months H3R3
2 months H3R3Z3E3 or 2 months H3R3Z3S3 (i.e 3=week)
New cases of smear-positive pulmonary TB
1
4 months HR
2 months HRZE or 2 months HRZS
Severe extra pulmonary TB
6 months HE† Severe smear-negative pulmonary TB
Severe concomitant HIV disease
5 months H3R3E3
2 months H3R3Z3E3 or 1 month H3R3Z3E
Previously treated smear-positive pulmonary TB
2
5 months HRE
2 months HRZES or 1 month HRZE
Relapse
Treatment failure
Treatment after default
4 months H3R3
2 months H3R3Z3E3
New cases of smear-negative pulmonary TB
3
4 months HR
2 months HRZE
Less severe extrapulmonary TB
6 months HE† S = streptomycin)
R = rifampicin; Z = pyrazinamide
(H = isoniazid;; E =ethambutol;


Ethambutol
Streptomycin
Pyrazinamide
Rifampicin
Isoniazid
Cell wall synthesis
Protein synthesis
Unknown
DNA transcription
Cell wall synthesis
Mode of action
Retrobulbar neuritis3Arthralgia
8th nerve damageRash
HepatitisGastrointestinal disturbanceHyperuricaemia
Febrile reactionsHepatitisRashGastrointestinal disturbance
Peripheral neuropathy1Hepatitis2Rash
Major adverse reactions
Peripheral neuropathyRash
NephrotoxicityAgranulocytosis
RashPhotosensitisationGout
Interstitial nephritisThrombocytopeniaHaemolytic anaemia
Lupoid reactionsSeizuresPsychoses
Less common adverse reactions

Managements and Chemotherapy

Quadruple therapy has become standard in the UK, although Ethambutol may be omitted under certain circumstances. Fixed-dose tablets combining two or three drugs are generally favoured: for example, Rifater (rifampicin, isoniazid and pyrazinamide) daily for 2 months, followed by 4 months of Rifinah (rifampicin and isoniazid). Streptomycin is rarely used in the UK, but is an important component of short-course treatment regimens in developing nations. Six months of therapy is appropriate for all patients with new-onset, uncomplicated pulmonary disease.

Managements and Chemotherapy

However, 9-12 months of therapy should be considered if the patient is HIV-positive, or if drug intolerance occurs and a second-line agent is substituted. Meningitis should be treated for a minimum of 12 months. Pyridoxine should be prescribed in pregnant women and malnourished patients to reduce the risk of peripheral neuropathy with isoniazid. Where drug resistance is not anticipated, patients can be assumed to be non-infectious after 2 weeks of appropriate therapy.

Managements and Chemotherapy

Most patients can be treated at home. . Admission to a hospital unit with appropriate isolation facilities should be considered where there is uncertainty about the diagnosis, intolerance of medication, questionable compliance, adverse social conditions or a significant risk of multidrug-resistant TB (MDR-TB: Culture-positive after 2 months on treatment, or contact with known MDR-TB). In choosing a suitable drug regimen, underlying comorbidity (renal and hepatic dysfunction, eye disease, peripheral neuropathy and HIV status), as well as the potential for drug interactions, must be considered.

Managements and Chemotherapy

Baseline liver function and regular monitoring are important for patients treated with standard therapy including rifampicin, isoniazid and pyrazinamide, as all of these agents are potentially hepatotoxic. Mild asymptomatic increases in transaminases are common but serious liver damage is rare. Women taking the oral contraceptive pill must be warned that its efficacy will be reduced and alternative contraception may be necessary. Ethambutol should be used with caution in patients with renal failure, with appropriate dose reduction and monitoring of drug levels. Adverse drug reactions occur in about 10% of patients, but are significantly more common in the presence of HIV co-infection .

Managements and Chemotherapy

Corticosteroids reduce inflammation and limit tissue damage, and are currently recommended when treating pericardial or meningeal disease, and in children with endobronchial disease. They may confer benefit in TB of the ureter, pleural effusions and extensive pulmonary disease, and can suppress hypersensitivity drug reactions. Surgery is still occasionally required (e.g. for massive haemoptysis, loculated empyema, constrictive pericarditis, lymph node suppuration, spinal disease with cord compression), but usually only after a full course of antituberculosis treatment

Control and prevention of TB

The effectiveness of therapy for pulmonary TB may be judged by a further sputum smear at 2 months and at 5 months. A positive sputum smear at 5 months defines treatment failure. Extrapulmonary TB must be assessed clinically or radiographically as appropriate. The WHO is committed to reducing the incidence of TB by 2015. Important components of this goal include supporting the development of laboratory and health-care services to improve detection and treatment of active and latent TB.


Detection of latent TB
It has the potential to identify the probable index case, other cases infected by the same index patient (with or without evidence of disease), and close contacts who should receive BCG vaccination (see below) or chemotherapy. Approximately 10-20% of close contacts of patients with smear-positive pulmonary TB and 2-5% of those with smear-negative, culture-positive disease have evidence of TB infection. Cases are commonly identified using the tuberculin skin test (Box 19.63 and Fig. 19.39). An otherwise asymptomatic contact with a positive tuberculin skin test but a normal chest X-ray may be treated with chemoprophylaxis to prevent infection progressing to clinical disease

Detection of latent TB

.Chemoprophylaxis is also recommended for children aged less than 16 years identified during contact tracing to have a strongly positive tuberculin test, children aged less than 2 years in close contact with smear-positive pulmonary disease, those in whom recent tuberculin conversion has been confirmed, and babies of mothers with pulmonary TB. It should also be considered for HIV-infected close contacts of a patient with smear-positive disease. Rifampicin plus isoniazid for 3 months or isoniazid for 6 months is effective

Directly observed therapy (DOT)

Poor adherence to therapy is a major factor in prolonged infectious illness, risk of relapse and the emergence of drug resistance. DOT involves the supervised administration of therapy thrice weekly and improves adherence. It has become an important control strategy in resource-poor nations. In the UK, it is currently only recommended for patients thought unlikely to be adherent to therapy: Those who are homeless, alcohol or drug users, drifters, those with serious mental illness and those with a history of non-compliance