Pulmonary non-tuberculous mycobacterial disease masquerading as recurrent tuberculosis in Nigeria: diagnostic complexities and therapeutic challenges from a 17-year longitudinal case report

Technical Summary: Pulmonary Non-Tuberculous Mycobacterial Disease Masquerading as Recurrent Tuberculosis in Nigeria

Problem Statement
Pulmonary non-tuberculous mycobacterial disease (NTM-LD) is an increasingly recognized cause of chronic pulmonary infection globally. However, in tuberculosis (TB)-endemic regions like Nigeria, NTM-LD remains significantly underdiagnosed. Clinical algorithms and laboratory infrastructures are primarily optimized for detecting Mycobacterium tuberculosis (MTBC). Consequently, patients with NTM-LD are frequently misdiagnosed as having recurrent or drug-resistant TB. This leads to repeated empirical anti-tuberculosis treatments, delayed appropriate management, unnecessary drug exposure, and progressive, irreversible structural lung damage. The clinical and radiological overlap between NTM-LD and TB, combined with the inability of standard acid-fast bacilli (AFB) microscopy to differentiate between the two, exacerbates these diagnostic challenges in resource-limited settings.

Methodology
This paper presents a 17-year longitudinal case report of an immunocompetent Nigerian male. The methodology involves a retrospective analysis of the patient's clinical history, diagnostic investigations, treatment courses, and long-term follow-up at the University of Port Harcourt Teaching Hospital (UPTH) and the Nigerian Institute of Medical Research (NIMR).

• Patient Profile: A 28-year-old male (at initial presentation in 2009) with a history of completed first-line anti-TB treatment in 2004.
• Diagnostic Workflow:
  • Initial Presentation (2009): Evaluation included sputum AFB microscopy (Ziehl–Neelsen), chest radiography, and full blood counts.
  • Empirical Treatment: Based on national guidelines (Category II regimen) for suspected relapsed TB, despite negative initial smears.
  • Re-evaluation (2010): Upon treatment failure and progressive radiographic destruction, repeat sputum microscopy was performed. The patient was referred to the National TB Reference Laboratory.
  • Advanced Diagnostics: Mycobacterial culture and molecular genotypic testing were conducted at NIMR to differentiate MTBC from NTM.
  • Differential Consideration: Chronic pulmonary aspergillosis (CPA) was considered due to cavitary disease, leading to empirical antifungal therapy (itraconazole) due to the unavailability of specific fungal serology.
  • Confirmation: Final diagnosis relied on culture growth of a non-tuberculous mycobacterium and molecular confirmation that the isolate was not part of the MTBC. Species-level identification and drug susceptibility testing (DST) were unavailable due to local laboratory limitations.

Key Results

• Clinical Course: The patient presented with chronic productive cough, weight loss, night sweats, and extensive unilateral fibrocavitary lung disease. Despite completing a Category II anti-TB regimen, symptoms persisted, and the left lung progressed to "destroyed lung syndrome" with chronic bronchiectasis.
• Microbiological Findings: Initial sputum smears were negative. Later, AFB was detected in one of two specimens, raising suspicion of drug-resistant TB. However, culture and molecular testing confirmed the isolate was a non-tuberculous mycobacterium, excluding MTBC.
• Therapeutic Outcome: Following the diagnosis of pulmonary NTM, the patient was treated with a regimen of rifampicin, clarithromycin, itraconazole, and zinc. This resulted in gradual clinical improvement and stabilization of constitutional symptoms.
• Long-term Sequelae: Despite clinical improvement, the patient suffered irreversible structural lung damage, resulting in a "destroyed left lung" and chronic bronchiectasis, requiring long-term respiratory follow-up.
• Diagnostic Limitations: The case highlighted the inability to perform species identification or DST locally, forcing reliance on empirical therapy based on the cultured isolate's general characteristics.

Key Contributions

• Diagnostic Complexity: The report illustrates the specific difficulties in distinguishing NTM-LD from recurrent TB in high-burden settings where clinical algorithms prioritize TB and lack NTM-specific pathways.
• Limitations of Standard Tools: It demonstrates the insufficiency of AFB microscopy alone, which can yield false positives for NTM (due to shared acid-fast properties) or false negatives, leading to diagnostic uncertainty.
• Consequences of Delay: The case documents the tangible consequences of delayed diagnosis, specifically the progression to destroyed lung syndrome and chronic bronchiectasis in an immunocompetent individual with prior TB history.
• Resource-Limited Reality: It provides a real-world example of how the lack of advanced molecular diagnostics and species identification in Nigeria impacts clinical decision-making, often necessitating empirical treatment for multiple potential pathogens (NTM and fungal).

Significance and Claims
The authors assert that this case highlights substantial diagnostic and therapeutic challenges for pulmonary NTM disease in resource-limited, TB-endemic settings. The paper claims that:

1. Reliance on Empirical TB Treatment is Flawed: Relying solely on clinical history and AFB microscopy for patients with persistent symptoms after TB treatment can lead to misdiagnosis and inappropriate therapy.
2. Need for Algorithm Integration: There is an urgent need to integrate NTM considerations into national TB diagnostic algorithms, particularly for patients with discordant microbiological findings or poor response to standard TB therapy.
3. Laboratory Capacity is Critical: Strengthening laboratory infrastructure to include mycobacterial culture, species identification, and drug susceptibility testing is essential for timely and accurate diagnosis.
4. Clinician Awareness: Improving clinician awareness regarding the possibility of NTM-LD in immunocompetent patients with prior pulmonary damage is necessary to reduce diagnostic delays.

The paper concludes that while the specific findings are from a single case, they underscore the broader systemic issues affecting the management of chronic mycobacterial lung disease in low- and middle-income countries. The authors do not claim to have solved the diagnostic gap but rather use the 17-year trajectory of this patient to advocate for systemic improvements in laboratory capacity and clinical vigilance.