Tuberculosis Pathogenesis Types Diagnosis and Treatment
What is tuberculosis?
Tuberculosis (phthísis, مرض السّل) is a highly contagious infectious disease caused by mycobacterium tuberculosis, which is acquired by inhaling a contaminated airborne droplet; However, infectivity is relevant to the duration of contact, experts agree that a contact via constant exposure within a period of two months is enough for the bacterial infection to develop in 95% of cases.
Inhaled microrganisms are deposited in the alveoli of lower lobes because they are best ventilated, they replicate once per 24hrs, and after that they gain access to the lymphatic channels, regional lymph nodes of the chest and pass through the thoracic duct to the bloodstream where they widespread, hematogenous dissemination may occur
What are the different types of tuberculosis?
Tuberculosis (TB) is classified into two types:
1- Initial TB (primary pulmonary tuberculosis or pulmonary tuberculosis) is the most common form of tuberculosis that occurs after inhaling airborne droplets contaminated with mycobacterium tuberculosis from a cough or sneeze of an infected person, it is characterized by bronchopneumonia of the lower lobes with regional lymph nodes and unilateral pleural effusion.
Commonly no symptoms occur at this stage, but a chest X-ray showing a solitary calcified nodule accompanied by hilar adenopathy may suggest the diagnosis if the patient had a positive PPD test (a positive TB skin test or TB blood test).
2- Reactivation TB disease occurs after years of harboring the microorganisms within the macrophages, reactivation may occur in sites rich with oxygen such as the upper lobes, the reactivation happens when immunity is suppressed or compromised (cell mediated immunity), especially in elderly patients (5th decade) due to age-related thymic involution (age-related thymus atrophy).
In most cases, reactivation TB disease occurs within the first two years post-infection.
What is latent tuberculosis infection
Latent tuberculosis infection (latent tuberculosis, LTB, or LTBI) is a condition in which a person is infected with mycobacterium tuberculosis, but the patient does not feel sick and remains asymptomatic (the patient does not have active tuberculosis).
What are the symptoms of tuberculosis?
Symptoms of active TB include:
- Weight loss
- Persistent cough that lasts three or more weeks.
- Weakness (fatigue)
- Dyspnea or shortness of breath
- Low grade fever
- Night sweats and chills
- Hemoptysis (coughing up blood)
How to diagnose tuberculosis and what are the diagnostic tests for tuberculosis?
How long after the injection should the skin test be read and how to properly read a ppd skin test?
1- PPD test or Mantoux test is a skin test in which five tuberculin units (0.1 ml) of purified protein derivative are injected under the skin. After 2-3 days, the patient must return for clinical evaluation and the doctor should inspect the injection site for local skin reactions, such as erythema (redness) or swelling to confirm the diagnosis, an induration >10 mm suggests a significant risk of being sick, an induration between 5-10 mm suggests that the diagnosed individual is in the group of high risk population to develop tuberculosis. In adults, if Mendel-Mantoux test is negative, it must be repeated.
How long does it take to get ppd results?
The patient has to wait for 2-3 days before diagnosis can be made by visual inspection of the injection site. Mantoux test should be read 2-3 days after the injection.
2- Chest x-ray and three sputum cultures, three morning sputum samples are stained for acid fast bacilus, nearly 50% of cases are diagnosed in this way.
How to treat tuberculosis?
Most patients will need a long course of treatment (usually six months).
High risk individuals with no active disease should receive:
1-Isoniazid 300g per day, orally for a period of 6-12 months
2- Rifampin pyrazinamide is a drug used to treat tuberculosis, patients must continue to take this drug for two months (a two months period treatment), until sensitivity test results are available, additional therapy for a period of four months is mandated if stains are sensitive to isoniazid and rifampin.
Pyridoxine 25-50 mg per day is given to prevent peripheral neuropathy from isoniazid.