Overview
Tuberculosis (TB) affecting the skin and subcutaneous tissue, known as cutaneous TB, represents a significant clinical entity within the broader spectrum of extrapulmonary TB. It manifests through various forms including scrofuloderma, lupus vulgaris, and acute forms like erythema induratum. Cutaneous TB primarily affects immunocompromised individuals, children, and those living in regions with high TB prevalence. Early recognition and management are crucial due to the potential for chronicity, disfigurement, and the risk of systemic spread. This condition underscores the importance of accurate clinical assessment and timely intervention in day-to-day practice to prevent complications and improve patient outcomes 1.Pathophysiology
The pathophysiology of cutaneous TB involves the hematogenous dissemination of Mycobacterium tuberculosis from primary pulmonary foci or reactivation of dormant bacilli. Once in the skin, the bacteria interact with local immune cells, particularly macrophages and lymphocytes, leading to granuloma formation. In chronic forms like lupus vulgaris, these granulomas may become organized into fibrous nodules, often resulting in characteristic skin lesions characterized by induration and scarring 1. The interaction between the mycobacteria and the extracellular matrix proteins, such as collagen, influences the microenvironment and cellular behavior within the affected tissue, potentially affecting healing and scarring processes 2. However, detailed molecular mechanisms specific to skin TB are less extensively studied compared to pulmonary TB, highlighting areas for further research.Epidemiology
Cutaneous TB exhibits variable incidence and prevalence, often reflecting regional TB burden and socioeconomic factors. It is more prevalent in low-income countries where TB control measures may be less effective 1. Age-wise, children and young adults are disproportionately affected, possibly due to developing immune systems or higher exposure risks. Geographic distribution tends to correlate with areas of high TB incidence, such as sub-Saharan Africa and parts of Asia. Risk factors include immunosuppression (e.g., HIV co-infection), malnutrition, and overcrowded living conditions. Trends over time show fluctuations tied to public health interventions and socioeconomic improvements, though consistent data across regions remain challenging to obtain 1.Clinical Presentation
Clinical presentations of cutaneous TB vary widely, from indolent, slowly progressive lesions to more acute forms. Typical manifestations include chronic, well-demarcated, hyperpigmented or atrophic plaques (lupus vulgaris), ulcerations with undermined borders (scrofuloderma), and nodular lesions that may ulcerate (acute forms like erythema induratum). Red-flag features include rapid progression, systemic symptoms (fever, weight loss), and signs of disseminated disease. Early recognition is critical to prevent extensive tissue damage and potential systemic spread. Accurate clinical assessment often requires a thorough history and physical examination, complemented by diagnostic investigations to confirm the diagnosis 1.Diagnosis
The diagnostic approach for cutaneous TB involves a combination of clinical evaluation, histopathological examination, and microbiological confirmation. Key steps include:Clinical Evaluation: Detailed history and physical examination focusing on lesion characteristics, duration, and associated symptoms.
Histopathology: Skin biopsy is essential, demonstrating granulomatous inflammation with caseating necrosis, which is highly suggestive of TB 1.
Microbiological Confirmation: Acid-fast bacilli (AFB) staining and culture of biopsy specimens are definitive. Polymerase Chain Reaction (PCR) can also be utilized for rapid detection 1.Specific Criteria and Tests:
Skin Biopsy: Required for histopathological examination.
AFB Staining: Positive findings in biopsy specimens confirm the presence of mycobacteria.
Culture: Growth of M. tuberculosis from biopsy samples confirms diagnosis.
PCR: Positive PCR for M. tuberculosis DNA supports diagnosis, especially when cultures are negative or delayed.
Differential Diagnosis: Conditions like sarcoidosis, fungal infections (e.g., chromoblastomycosis), and malignancies (e.g., squamous cell carcinoma) must be ruled out based on clinical features and laboratory findings 1.Differential Diagnosis
Sarcoidosis: Granulomas without caseation necrosis; often associated with systemic symptoms and bilateral hilar lymphadenopathy on imaging.
Fungal Infections: Characterized by specific histopathological features (e.g., septate hyphae in fungal infections) and culture results.
Malignancies: Biopsy findings showing malignant cells with atypical nuclei and absence of granulomatous inflammation.Management
First-Line Treatment
Antitubercular Therapy (ATT): Standard regimen includes isoniazid, rifampicin, pyrazinamide, and ethambutol for the initial 2 months (intensive phase), followed by isoniazid and rifampicin for an additional 4-7 months (continuation phase).
- Doses: Isoniazid 5-10 mg/kg/day, Rifampicin 10-20 mg/kg/day, Pyrazinamide 20-30 mg/kg/day, Ethambutol 15-20 mg/kg/day.
- Monitoring: Regular liver function tests, complete blood count, and clinical assessment for adverse effects.
- Contraindications: Known hypersensitivity to ATT drugs, severe liver disease 1.Second-Line Treatment
Reserved for Multidrug-Resistant TB (MDR-TB): Includes fluoroquinolones (e.g., moxifloxacin), second-line injectables (e.g., amikacin), and other agents like para-aminosalicylic acid (PAS).
- Doses: Moxifloxacin 400 mg daily, Amikacin 15 mg/kg/day, PAS 30 mg/kg/day.
- Monitoring: Frequent renal function tests, hearing assessments (for ototoxicity), and regular clinical evaluations.
- Contraindications: Renal impairment, hearing loss, or other drug interactions 1.Refractory Cases
Specialist Referral: For persistent or worsening lesions despite appropriate ATT, referral to an infectious disease specialist is warranted.
- Considerations: Genetic susceptibility testing, advanced imaging, and further microbiological analysis.
- Management: Tailored therapy based on resistance patterns and clinical response 1.Complications
Chronic Scarring and Disfigurement: Common in chronic forms like lupus vulgaris.
Systemic Spread: Risk of hematogenous dissemination leading to extrapulmonary TB involvement.
Adverse Drug Reactions: Hepatotoxicity, peripheral neuropathy, and visual disturbances are potential complications of ATT.
When to Refer: Persistent lesions unresponsive to initial therapy, signs of systemic involvement, or severe adverse drug reactions necessitate prompt referral to specialists for further management 1.Prognosis & Follow-Up
The prognosis for cutaneous TB is generally good with appropriate treatment, though chronicity can lead to significant morbidity. Prognostic indicators include early diagnosis, adherence to therapy, and absence of underlying immunosuppression. Follow-up intervals typically involve:
Monthly Clinical Assessments: Monitoring for lesion resolution and adverse drug reactions.
Biopsy and Culture Follow-Up: Periodic reevaluation if initial cultures are pending or if there is suspicion of treatment failure.
Liver Function Tests: Every 2-3 months during ATT to monitor for hepatotoxicity 1.Special Populations
Pediatrics: Children may present with atypical forms and require careful monitoring for growth and development impacts of ATT.
Immunocompromised Individuals: Higher risk of disseminated disease; close follow-up and possibly extended treatment durations are necessary.
HIV Co-Infection: Increased susceptibility to TB and potential for more aggressive disease; antiretroviral therapy (ART) should be integrated into management plans 1.Key Recommendations
Perform a Skin Biopsy for Definitive Diagnosis (Evidence: Strong 1)
Initiate Standard ATT Regimen for Confirmed Cases (Evidence: Strong 1)
Monitor for Adverse Drug Reactions Regularly (Evidence: Moderate 1)
Refer Patients with Refractory or Disseminated Disease to Specialists (Evidence: Moderate 1)
Consider HIV Testing in All Suspected Cases (Evidence: Moderate 1)
Ensure Adherence Support for Long-Term Treatment (Evidence: Expert opinion)
Evaluate for and Manage Complications Promptly (Evidence: Moderate 1)
Follow-Up with Regular Clinical Assessments and Laboratory Tests (Evidence: Moderate 1)
Tailor Treatment Based on Resistance Patterns in MDR-TB Cases (Evidence: Moderate 1)
Provide Psychological Support for Patients with Significant Disfigurement (Evidence: Expert opinion)References
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4 Naaldijk Y, Friedrich-Stöckigt A, Sethe S, Stolzing A. Comparison of different cooling rates for fibroblast and keratinocyte cryopreservation. Journal of tissue engineering and regenerative medicine 2016. link