What are the cutaneous markers of tuberculosis (TB)?

Cutaneous Markers of Tuberculosis

The main cutaneous markers of tuberculosis include lupus vulgaris, scrofuloderma, tuberculosis verrucosa cutis, tuberculous chancre, orificial tuberculosis, miliary tuberculosis, metastatic tuberculous abscess, and tuberculids such as lichen scrofulosorum and erythema induratum of Bazin. 1

Primary Forms of Cutaneous TB

Cutaneous tuberculosis represents approximately 1-1.5% of all extrapulmonary tuberculosis cases 2. The clinical presentation varies widely depending on the route of infection, immune status of the patient, and previous sensitization to tuberculosis.

The main cutaneous manifestations include:

1. Lupus Vulgaris

   • Most common form of cutaneous TB 3
   • Occurs in previously sensitized individuals with moderate immunity against TB
   • Presents as reddish-brown plaques that expand peripherally
   • May develop into ulcerative, vegetative, papular, nodular or tumor forms
   • Shows apple-jelly nodules on diascopy (pressing with a glass slide)
   • Histologically shows non-caseating granulomas with Langhan's giant cells

2. Scrofuloderma

   • Results from contiguous spread from underlying tuberculous lymphadenitis
   • Presents as firm subcutaneous nodules that eventually ulcerate
   • Commonly affects cervical, submandibular, and supraclavicular regions
   • Heals with characteristic puckered scarring

3. Tuberculosis Verrucosa Cutis

   • Occurs through direct inoculation in previously sensitized individuals
   • Presents as warty, verrucous plaques typically on hands, knees, or buttocks
   • Also known as "prosector's wart" or "anatomist's wart"

4. Tuberculous Chancre

   • Primary inoculation tuberculosis in non-sensitized individuals
   • Presents as a firm, painless nodule that ulcerates
   • Regional lymphadenopathy is common

5. Orificial Tuberculosis

   • Occurs at mucocutaneous junctions in patients with advanced internal TB
   • Painful, rapidly ulcerating lesions

6. Miliary Tuberculosis

   • Hematogenous dissemination in immunocompromised patients
   • Multiple small papules or pustules

7. Metastatic Tuberculous Abscess

   • Cold abscesses from hematogenous spread
   • Fluctuant, non-tender subcutaneous nodules

Tuberculids

These represent hypersensitivity reactions to TB antigens in patients with high immunity:

1. Lichen Scrofulosorum

   • Small, firm, follicular or perifollicular papules
   • Asymptomatic, often on trunk

2. Papulonecrotic Tuberculid

   • Recurrent crops of symmetrical papules that undergo necrosis
   • Typically on extremities

3. Erythema Induratum of Bazin

   • Tender, subcutaneous nodules on posterior calves
   • May ulcerate and heal with scarring

Diagnostic Approach

The diagnosis of cutaneous TB requires correlation of clinical findings with diagnostic testing 1:

1. Tuberculin Skin Test (TST)

   • Usually strongly positive in cutaneous TB
   • Interpretation based on induration size:
     • ≥5 mm: HIV-positive persons, recent contacts of TB cases
     • ≥10 mm: Persons with clinical risk factors
     • ≥15 mm: Persons with no risk factors 4

2. Histopathology

   • Shows granulomatous inflammation
   • Multibacillary forms show acid-fast bacilli
   • Paucibacillary forms may not show organisms 5

3. Microbiological Testing

   • Acid-fast bacilli staining
   • Culture for M. tuberculosis
   • PCR for M. tuberculosis DNA

Clinical Pearls and Pitfalls

• Cutaneous TB should be suspected in chronic, non-healing skin lesions, especially in endemic areas or in immunocompromised patients
• Multiple clinical forms may coexist in the same patient 2, 6
• Diagnosis can be challenging in paucibacillary forms where organisms are difficult to demonstrate
• BCG vaccination history should not exclude the diagnosis of cutaneous TB 4
• Treatment follows the same principles as pulmonary TB with multi-drug regimens

Management

Treatment of cutaneous TB follows standard anti-tuberculous therapy protocols, typically including isoniazid, rifampin, ethambutol, and pyrazinamide for the initial phase, followed by isoniazid and rifampin for the continuation phase 1.

Surgical drainage may be required for cold abscesses associated with cutaneous TB 6.

The prognosis is generally good with appropriate treatment, though extensive disease may result in significant scarring.