Tuberculosis (pulmonary): Clinical sciences

Pulmonary tuberculosis, or pulmonary TB, is an infectious disease of the lungs caused by Mycobacterium tuberculosis. Primary infection with M. tuberculosis in adults is usually asymptomatic and followed by a latent phase, which, in some cases, can progress to active pulmonary tuberculosis, also called reactivation or post-primary tuberculosis.

The gold standard for diagnosing pulmonary tuberculosis is mycobacterial culture, but preliminary diagnosis can be made with acid-fast bacilli smear and rapid nucleic acid amplification testing.

Diagnostic testing should also include drug susceptibility testing, to identify cases of multi- and extensively-drug resistant tuberculosis.

Now, if you suspect pulmonary TB, first, you should perform an ABCDE assessment to determine if your patient is unstable or stable. If the patient is unstable, stabilize their airway, breathing, and circulation, which might require intubation. Additionally, obtain IV access, administer supplemental oxygen, and put your patient on continuous vital sign monitoring, including heart rate, blood pressure, and pulse oximetry.

Now, let’s go back to the ABCDE assessment and take a look at the stable patients. In this case, perform a focused history and physical examination and get a chest x-ray.

History typically reveals respiratory involvement, such as chronic cough and hemoptysis, but also systemic symptoms, like unintentional weight loss, anorexia, fever, and night sweats.

Additionally, the individual might present with risk factors for exposure to tuberculosis, such as living in a facility like a nursing home, homeless shelter, or correctional facility; having a family member or close contact with tuberculosis; or spending time in a country with a high prevalence of TB.

Also, the patient could report risk factors for developing active tuberculosis, like being immunocompromised due to HIV, malignancy, or immunosuppressive therapy.

Now, here’s one clinical pearl to keep in mind! Individuals with HIV are much more likely to develop active tuberculosis compared to people without HIV.

Patients who are diagnosed with active tuberculosis should be tested for HIV, and HIV positive patients should be started on antiretroviral therapy, in addition to treatment for TB.

On the other hand, physical exam might reveal lung findings, such as dullness to percussion; low-pitched, hollow breath sounds; and rales, or crackles.

The chest x-ray will typically show a solitary cavitary lesion, called a Ghon focus, in addition to other scattered consolidation or nodularity.

On the other hand, a Ghon complex is when a Ghon focus presents together with ipsilateral hilar lymphadenopathy.

Lastly, a Ranke complex is a later manifestation of a Ghon complex, where the lesion undergoes calcification and has an ipsilateral calcified lymph node.

As a clinical pearl, a CT scan is not usually required to diagnose TB, but it can be ordered in unclear cases to obtain a more precise resolution of the cavitary lesions.

Here’s a high-yield fact for your tests! The cavitary lung lesions, in patients with tuberculosis, classically involve the upper lobes, but less frequently may involve the lower lobes too.

Also, remember that several differential diagnoses should come to mind when a question stem mentions cavitary lung lesions, such as aspergillus infection, sarcoidosis, or even cancer, so the clinical history is what will help you narrow down the diagnosis.

If these findings are present, you should suspect pulmonary TB and order laboratory testing of the patient’s sputum. Check rapid diagnostic tests including smear microscopy for acid fast bacilli, or AFB, on 3 separate sputum samples, and order nucleic acid amplification testing or NAAT for short.

In addition, send a sputum sample for mycobacterial culture. Mycobacterial culture of sputum, bronchoalveolar lavage, pleural fluid, or even pleural or lung biopsy is the gold standard for diagnosing tuberculosis,

but culture results may not be available for weeks. On the other hand, results of the AFB smear and nucleic acid amplification testing are ready in 1 to 2 days, which can help expedite diagnosis and treatment.

Ok, let’s say the sputum AFB is positive and NAAT is positive. Then, you can diagnose the patient with pulmonary TB.