From the Guidelines
Interface dermatitis caused by lung mycobacterium infection is best diagnosed through a combination of clinical evaluation, radiographic findings, and laboratory tests, including acid-fast bacilli (AFB) smears and cultures for mycobacteria, as well as a purified protein derivative (PPD)-tuberculin skin test, as recommended by the American Thoracic Society/Infectious Diseases Society of America 1.
Diagnosis Approach
For diagnosing interface dermatitis caused by lung mycobacterium infection:
- Clinical evaluation should include epidemiologic information, clinical, pathological, and radiographic findings.
- Laboratory tests should include AFB smears and cultures for mycobacteria.
- A PPD-tuberculin skin test may be done at the time of initial evaluation, but a negative result does not exclude the diagnosis of active tuberculosis.
Key Considerations
- The decision to initiate combination antituberculosis chemotherapy should be based on epidemiologic information, clinical, pathological, and radiographic findings, and the results of microscopic examination of AFB-stained sputum and cultures for mycobacteria.
- If the suspicion of tuberculosis is high or the patient is seriously ill, combination chemotherapy using one of the recommended regimens should be initiated promptly, often before AFB smear results are known and usually before mycobacterial culture results have been obtained.
- A positive AFB smear provides strong inferential evidence for the diagnosis of tuberculosis, and if the diagnosis is confirmed by isolation of M. tuberculosis or a positive nucleic acid amplification test, treatment can be continued to complete a standard course of therapy.
Diagnostic Challenges
- The diagnosis of interface dermatitis caused by lung mycobacterium infection can be challenging due to the similarity in clinical and radiographic presentations with other conditions.
- The PPD-tuberculin skin test has limitations, including false-positive results due to previous BCG vaccination or infection with nontuberculous mycobacteria.
- The interpretation of skin-test reactions requires knowledge of tuberculin-test sensitivity and specificity, as well as positive predictive value, as discussed in the American Thoracic Society/Centers for Disease Control and Prevention/Infectious Diseases Society of America statement on targeted tuberculin testing and treatment of latent tuberculosis infection 1.
From the Research
Diagnosis of Interface Dermatitis Caused by Pulmonary Mycobacterium Infection
The diagnosis of interface dermatitis caused by pulmonary Mycobacterium infection involves a combination of clinical, epidemiological, and laboratory investigations.
- A clinical examination to identify symptoms such as fever, malaise, and skin lesions 2
- A purified protein derivative (PPD) skin test to detect the presence of Mycobacterium tuberculosis 2
- Imaging studies such as ultrasound, CT, or MRI to evaluate lymph node masses 2
- A lymph node biopsy to confirm the diagnosis of tuberculosis (TB) and polymerase chain reaction (PCR) to identify the type of Mycobacterium 2
- Culture of the Mycobacterium to determine its susceptibility to antibiotics 3, 4, 5
Laboratory Investigations
Laboratory investigations play a crucial role in the diagnosis of interface dermatitis caused by pulmonary Mycobacterium infection.
- Acid-fast bacilli staining to detect the presence of Mycobacterium 3, 4
- Culture in solid or liquid media to isolate the Mycobacterium 3, 4
- Molecular assays such as PCR to confirm the diagnosis and identify the type of Mycobacterium 3, 4
- Histopathological examination of skin lesions to identify characteristic features of Mycobacterium infection 2, 4
Differential Diagnosis
The differential diagnosis of interface dermatitis caused by pulmonary Mycobacterium infection includes other conditions that can cause similar symptoms, such as: