Primary complex of cutaneous tuberculosis: causes, symptoms, diagnosis, and treatment

Primary complex of cutaneous tuberculosis, also known as tuberculous chancre, is the first cutaneous tuberculosis in patients who have never been infected with various types of tuberculosis, and have no acquired immunity against tuberculosis, more common in children, mostly through minor trauma in the skin.


Primary complex of cutaneous tuberculosis is caused by the inoculation of mycobacterium tuberculosis to the skin of healthy persons without natural or artificial immunity, more common in children. It is speculated that mycobacterium tuberculosis enters the skin through tiny wounds in the face and extremities or scratched areas in children. Primary complex of cutaneous tuberculosis often occurs after circumcision, improperly sterilized injection, wounds, surgery, ear piercing, and mouth-to-mouth resuscitation. When tuberculosis is prevalent in the community, the disease may occur after any part of human body exposed to sputa containing bacteria. In Asia, Primary complex of cutaneous tuberculosis is a common form of cutaneous tuberculosis.

Signs and Symptoms

Initial lesion is a brown papule, developing into a nodule or plaque, forming superficial, poorly demarcated ulcers, with undermined edges, with crusts, with basal granular bleeding surface, without subjective symptoms, with negative results in tuberculin test. Nearby lymph nodes can be swollen in 3 - 6 weeks. The swollen lymph nodes soften and rupture within 3 - 6 months, and caseous necrosis occurs, forming sinus tracts, with positive results in tuberculin test. In the absence of a history of obvious trauma, the initial lesion can be very small, with silver grey scales in the center, and an apple jelly nodule may be present. Surface healing can mask active infections at the base and adjacent lymphadenopathy may be present. Occasionally, lupoid nodules or scrofuloderma-like skin lesions are found around the cured ulcer. Skin lesions similar to paronychia have also been reported. Ocular edema and irritation can occur when the conjunctiva is involved. Oral lesions are rare, but can still occur and are painless. Alveolar and gingival mucosa can be invaded. Primary lesions can heal, but may develop into lupus vulgaris, occasionally with mild fever at onset. 10% of patients have nodular erythema. Occasionally, miliary tuberculosis and papulonecrotic tuberculids can occur.

The disease occurs mostly in the face and extremities, as well as in the mucosa in about 1/3 of patients.


Early changes are acute neutrophil infiltration, accompanied by necrosis. Many inflammatory cells and some mycobacterium tuberculosis can be seen. Granuloma is formed in 3 - 6 weeks, caseous necrosis occurs, and mycobacterium tuberculosis gradually disappears. The results of tuberculin test turn from negative to positive.


On the basis of the clinical features of rash and the adjacent lymph nodes enlargement, especially in children, primary complex of cutaneous tuberculosis should be highly suspected. A small scar or lupoid macule can be found in careful examinations. Positive results in bacteriological smear and culture can assist in the definitive diagnosis.

Missed diagnosis may occur if skin lesions are in the perianal and genital area, especially in children.


The disease is mainly caused by the infection of extrinsic mycobacterium tuberculosis, and the early single lesion can be surgically removed.

Topical isoniazid powder or 5% isoniazid ointment can be applied.

Systemic anti-tuberculosis treatment is necessary.

First-line anti-tuberculosis drugs include isoniazid (INH), rifampicin (RIF), pyrazinamide (PZA), and ethambutol (EMB). These drugs should be treated in combination.

Second-line anti-tuberculosis drugs are often used in drug-resistant tuberculosis patients or patients unable to tolerate first-line drugs, mainly including aminoglycosides and fluoroquinolones, such as streptomycin, kanamycin, amikacin, capreomycin, levofloxacin, and moxifloxacin. Aminoglycosides are only for parenteral use.

Other second-line drugs include ethionamide, cycloserine, and para-aminosalicylic acid, with anti-tuberculosis effect weaker than first-line drugs, with strong toxicity, but effective against drug-resistant tuberculosis.

Bedaquiline, delamanid, and sutezolid are new anti-tuberculosis drugs and are usually reserved for extensively drug-resistant tuberculosis, or patients unable to tolerate other second-line drugs.