Cutaneous Tuberculosis: Types, Diagnosis, And Treatment Guide

Cutaneous tuberculosis (CTB), also known as skin tuberculosis, is an uncommon manifestation of tuberculosis (TB) infection outside the lungs, representing 1.5–3% of extrapulmonary TB cases worldwide. It arises from infection of the skin by Mycobacterium tuberculosis, the primary causative bacterium of pulmonary TB, or rarely Mycobacterium bovis.

What is Cutaneous Tuberculosis?

Cutaneous tuberculosis results from the invasion of skin or mucous membranes by mycobacteria, leading to a spectrum of clinical presentations ranging from ulcers and nodules to plaques and verrucous lesions. While pulmonary TB remains the most common form, CTB often mimics other dermatological or neoplastic conditions, complicating diagnosis. It can occur via direct inoculation, contiguous spread from underlying foci, haematogenous dissemination, or as hypersensitivity reactions known as tuberculids.

In high-TB-prevalence areas, CTB is more frequent, but globally, it is rare due to effective control measures like BCG vaccination and milk pasteurization reducing M. bovis transmission. Immunocompromised individuals, such as those with HIV, face higher risks.

Who Gets Cutaneous Tuberculosis?

CTB affects individuals of all ages but shows patterns based on form. Children commonly develop scrofuloderma from contiguous spread, while adults are prone to paucibacillary forms like lupus vulgaris in previously sensitized individuals. Risk factors include TB-endemic regions, immunosuppression (HIV, diabetes), close contact with active TB cases, and skin trauma facilitating inoculation. Historically, M. bovis from unpasteurized milk contributed, now rare in developed countries.

Causes of Cutaneous Tuberculosis

The primary cause is Mycobacterium tuberculosis, a slow-growing acid-fast bacillus. Less commonly, M. bovis or BCG strain post-vaccination. Infection modes include:

• Exogenous (direct inoculation): Entry via skin breaks from infected sputum, needles, or piercings in unsensitized hosts, causing primary forms like tuberculous chancre.
• Endogenous contiguous spread: From underlying lymph nodes, bones, or joints (e.g., scrofuloderma).
• Haematogenous/autoinoculation: Spread from distant foci, leading to miliary or secondary forms.
• Hypersensitivity (tuberculids): Immune reactions to distant antigens without viable bacilli.

Types of Cutaneous Tuberculosis

CTB is classified into true TB (with bacilli demonstrable) and tuberculids (paucibacillary or hypersensitivity). Key types include:

• Tuberculous chancre (primary inoculation TB): Firm papule evolving to painless ulcer with undermined edges, 2–4 weeks post-inoculation. Common on face, extremities; regional lymphadenopathy follows. Predominantly in children.
• TB verrucosa cutis: Verrucous plaque from inoculation in sensitized individuals, often on feet (‘rasher’s nail’). Hyperkeratotic with microabscesses.
• Lupus vulgaris: Commonest paucibacillary form; apple-jelly nodules on ear, nose, cheeks. Chronic, leads to scarring/atrophy. In previously exposed adults.
• Scrofuloderma: Subcutaneous nodules ulcerating over infected nodes/bones. Most common multibacillary form in children; purulent sinuses. Neck, axillae affected.
• Miliary TB: Disseminated millet-seed papules from haematogenous spread; severe in immunocompromised.

Tuberculids (hypersensitivity):

• Papulonecrotic tuberculid (PNT): Recurrent necrotic papules on limbs.
• Lichen scrofulosorum (LS): Follicular papules in children.
• Erythema induratum (Bazin’s disease): Nodular vasculitis on calves.

Clinical Features

Presentations vary:

• Multibacillary: Ulcers (chancre), verrucous plaques (TVC), suppurating nodules/sinuses (scrofuloderma).
• Paucibacillary: Plaques/nodules (lupus vulgaris), disseminated papules (miliary).
• Tuberculids: Symmetric papules, nodules with necrosis/vasculitis.

Lesions are often asymptomatic initially but may itch, ulcerate, or scar. Systemic symptoms (fever, weight loss) if disseminated.

Complications

Untreated CTB leads to:

• Extensive scarring, contractures (lupus vulgaris).
• Squamous cell carcinoma in chronic lesions.
• Lymphatic/bone involvement.
• Systemic dissemination in immunocompromised patients.

Diagnosis

Diagnosis combines history, exam, and tests:

• Clinical suspicion: TB exposure, endemic area, morphology.
• Tuberculin skin test (TST)/IGRA: Positive in sensitized; IGRA preferred post-BCG.
• Biopsy: Tuberculoid granulomas, caseation necrosis, Langhans giant cells. AFB stain (Ziehl-Neelsen), culture, NAAT (PCR).
• Imaging: Chest X-ray, sputum culture for pulmonary involvement.
• FNAC: For scrofuloderma.

Histopathology: Early suppurative, later granulomatous with necrosis.

Differential Diagnoses

Treatment

Standard multi-drug anti-TB therapy (ATT):

• Intensive phase (2 months): Isoniazid (H), Rifampicin (R), Pyrazinamide (Z), Ethambutol (E) daily.
• Continuation phase (4–7 months): HR twice weekly or daily, extended for bone/joint involvement.

Total 6–9 months for sensitive TB; longer for resistant. Single-drug avoided. Surgery for localized recalcitrant lesions (excision, reconstruction). Monitor for resistance via culture/NAAT. Latent TB: Preventive isoniazid.

Outcome

Excellent with adequate ATT; lesions heal slowly, may scar. Relapse rare if compliant. Drug-resistant cases prolong treatment.

Prevention

BCG vaccination, TB control, pasteurization, contact tracing, protective measures in endemic areas.

Frequently Asked Questions

What causes skin TB?

Skin TB is caused by M. tuberculosis entering via inoculation, spread, or dissemination.

Is cutaneous TB contagious?

Directly from skin lesions rarely; more from pulmonary source.

How is CTB diagnosed?

Via biopsy, AFB stain, culture, NAAT, and IGRA/TST.

What is the treatment duration?

Typically 6–9 months of multi-drug therapy.

Can CTB lead to cancer?

Chronic lesions like lupus vulgaris may develop squamous cell carcinoma.

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medha deb

 

Medha Deb is an editor with a master's degree in Applied Linguistics from the University of Hyderabad. She believes that her qualification has helped her develop a deep understanding of language and its application in various contexts.

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