Cutaneous tuberculosis is a direct infection of the skin and mucous membranes by Mycobacterium tuberculosis or damage that occurs due to the spread of tubercle bacilli from other internal organs of the body and deep tissue tuberculosis lesions in the skin via lymphatic vessels or bloodstream. The occurrence and development of the disease are related to the nutritional status of the patient, the hygienic conditions and the resistance of the organism to the tuberculosis bacilli, the number of invading bacteria, etc. The incidence of extrapulmonary tuberculosis accounts for about 10% of all pulmonary tuberculosis, while skin tuberculosis is only a small part of extrapulmonary tuberculosis, and is less common than bone and joint tuberculosis or genitourinary tuberculosis. Second, the etiology and pathogenesis: skin tuberculosis is caused by direct invasion of tubercle bacilli into the skin and mucous membranes. 70% to 90% of the cases are caused by human tuberculosis, and 5% to 25% are caused by bovine tuberculosis. Occasionally, atypical Mycobacterium tuberculosis and BCG vaccine cause the disease. 1, exogenous infection: due to skin or mucous membrane injury, direct contact with Mycobacterium tuberculosis or bacterial sputum, urine, feces or toys, utensils and infection, such as anatomical warts, tuberculous warts, warty skin tuberculosis and BCG vaccination after dissection of a cadaver with tuberculosis. 2, endogenous infection: Mycobacterium tuberculosis through the blood or lymphatic system, from the internal organs or deep in the tissue of the tuberculosis foci spread to the mucous membrane of the skin and disease, bloodstream infection, such as cornual skin tuberculosis, common lupus and a variety of tuberculosis rash; lymph node reflux infection such as lymph node tuberculosis caused by common lupus; focal collapse caused by lymph node or bone, joint tuberculosis caused by scrofulous skin tuberculosis; focal direct spread of the disease, such as ulcerative cutaneous tuberculosis around the cavity. Cutaneous tuberculosis is not confined to the skin but is part of systemic tuberculosis. About one-third of cutaneous tuberculosis is associated with tuberculosis of other systems, such as pulmonary tuberculosis, lymphatic tuberculosis, and bone tuberculosis, with pulmonary tuberculosis being the most common. Pathology: The pathology of cutaneous tuberculosis is generally consistent with that of tuberculosis in other tissues, except that caseous changes, fibrosis and calcification rarely occur in tuberculous nodules. The degree of caseous changes varies among skin tuberculosis, with caseous necrosis being evident in tuberculous primary sores and scrofulous skin tuberculosis, less common in verrucous skin tuberculosis, and sclerosing erythema seen in about half of cases. Tuberculous nodules in the skin are composed mainly of epithelioid cells, while those in other tissues are composed mainly of lymphocytes. In tuberculous primary sores, there are nonspecific inflammatory changes in their early stages, while typical tuberculous nodules form after 3 to 6 weeks, and tubercle bacilli are not easily found in the nodules. In cornual and cavernous tuberculosis, there is no typical tuberculous nodule formation. In scrofulous cutaneous tuberculosis, the skin tissue is destroyed by nonspecific abscesses and ulcers, and tuberculous nodules and caseous necrosis appear at the margins of the lesions, with tuberculous bacteria visible on close examination. Warty skin tuberculosis is often not typically seen, but there is marked hyperkeratosis of the epidermis, hypertrophy of the spinous layer and papillomatous changes, marked neutrophil and lymphocytic infiltration of the dermis, visible giant cells, few typical tuberculous nodules, rare caseous necrosis, and difficulty in finding Mycobacterium tuberculosis. The typical changes in common lupus are the formation of tuberculosis nodules, epithelioid nodules surrounded by lymphocytes, caseous necrosis is usually rare or absent, and although Mycobacterium tuberculosis can be obtained by guinea pig inoculation, it is difficult to find in the biopsy tissue. Classification of cutaneous tuberculosis 1. inoculated cutaneous tuberculosis (exogenous): (1) tuberculous primary sores; (2) primary inoculated tuberculosis; (3) warty cutaneous tuberculosis; (4) common lupus (some) 2. secondary cutaneous tuberculosis (endogenous): (1) contact extension: scrofulous cutaneous tuberculosis; (2) self-inoculated cavernous cutaneous tuberculosis 3. hematogenous cutaneous tuberculosis: disseminated cornu Cutaneous tuberculosis, common lupus (some), tuberculous gumbo, migratory tuberculous abscess 4. Rash tuberculosis (tuberculous rash): (1) small papular: scrofulous moss; (2) papular: papular necrotizing tuberculous rash; (3) nodular: sclerosing erythema; (4) nodular tuberculous vasculitis 5. The diagnosis of cutaneous tuberculosis is based on: (1) typical clinical manifestations; (2) the presence of concomitant tuberculosis lesions of internal organs or other organs; (3) tuberculin test; (4) examination of tuberculosis bacteria in skin lesions; (5) histopathological examination; (6) the efficacy of anti-tuberculosis treatment, etc. Clinical manifestations Different types of skin tuberculosis have common features as well as their own characteristics in terms of their appearance, prevalent sites and their processes. Clinical symptoms: Skin tuberculosis can be accompanied by fever, fatigue, night sweats, poor nutrition and other symptoms of tuberculosis toxicity. Primary and reinfected skin tuberculosis is a chronic process, while various tuberculosis rashes occur in batches. 2, skin damage: skin damage of skin tuberculosis has its own characteristics, and recognizing these characteristics helps in diagnosis. (1) Applesauce nodules: The nodules are reddish-brown and soft, and the characteristic yellowish-red-brown color, similar to applesauce, is seen by pressure diagnosis with a slide, so they are called applesauce nodules. It is commonly seen in common lupus, which is one of its characteristic lesions, and also in facial disseminated lupus cornea. However, this nodule is not unique to cutaneous tuberculosis, as nodular disease, leprosy, syphilis, and deep mycosis can all have similar damage. (2) Ulceration: seen in scrofulous cutaneous tuberculosis, common lupus, and ulcers of cavernous tuberculosis with subterranean margins, necrosis at the base, irregular granulation tissue, and pallor that bleeds easily. (3) Papules: Facial disseminated cornual lupus, papular necrotizing tuberculosis rash, penile tuberculosis rash, scrofulous moss, disseminated cornual skin tuberculosis, etc., all have predominantly papular damage. (4) Scars: papulonecrotic tuberculosis rash leaves depressed scars after fading, sclerosing erythematous ulcers leave depressed pale scars after healing, and new lupus nodules can be regenerated on the scars, and scrofulous skin tuberculosis ulcers can form uneven lock-like scars after healing. 3. Preferred sites: All kinds of skin tuberculosis have their specific preferred sites. (1) Face: Commonly seen in common lupus, facial disseminated milky lupus, and occasionally in warty skin tuberculosis. (2) Neck: Scrofulous skin tuberculosis is the most common. (3) Trunk: common in scrofulous lichen planus and disseminated milia cutaneous tuberculosis, also seen in scrofulous cutaneous tuberculosis. (4) Extremities: seen in papulonecrotic tuberculosis rash, verrucous skin tuberculosis, sclerosing erythema and tuberculous primary sores. (5) Skin-mucosal junction: seen in cavernous tuberculosis and common lupus. (6) External genitalia: seen in penile tuberculosis rash, scrofulous skin tuberculosis and common lupus. (2) Concomitant visceral tuberculosis: In any patient suspected of cutaneous tuberculosis, examination of other sites should not be neglected to detect tuberculous lesions outside the skin. In addition to routine X-ray examination, superficial lymph nodes must be touched, epididymis in men and adnexa in women should not be neglected, and abdominal ultrasound examination is also of some significance. The diagnosis of extracutaneous tuberculosis also contributes to the diagnosis of cutaneous tuberculosis. (C) Mycobacterium tuberculosis examination: The examination of Mycobacterium tuberculosis can be carried out by antacid staining of lesions or ulcerated tissues in prints, smears of secretions or tissue sections, and a positive culture of Mycobacterium tuberculosis is the gold standard for diagnosis. In true cutaneous tuberculosis, such as tuberculous primary sores, common lupus, scrofulous cutaneous tuberculosis, and cavernous tuberculosis disseminated cornified cutaneous tuberculosis, antacid bacilli can be detected in the skin lesions. In recent years, molecular diagnostic techniques have been developed rapidly, and PCR techniques can be applied to the diagnosis of cutaneous tuberculosis. (d) Histopathological examination: taking biopsies for histopathological examination is an important tool in the diagnosis of cutaneous tuberculosis. When the skin has a variety of lesions, two or more specimens with different manifestations should be taken so that the correct diagnosis can be made as soon as possible. (E) Tuberculin test: Over the years, skin scientists have applied the combined bacteriocin test to detect delayed hypersensitivity reactions in patients with cutaneous tuberculosis and found that patients with common lupus, warty skin tuberculosis, and scrofulous skin tuberculosis mostly showed positive reactions, while patients with cornified tuberculosis showed false negative reactions, the former being called increased reactivity and the latter being called non-reactivity. (a) Systemic chemotherapy: Chemotherapy for cutaneous tuberculosis also follows the principles of “early, regular, complete, combined and appropriate” chemotherapy for pulmonary tuberculosis. Any treatment of skin tuberculosis should be a holistic treatment, and potential tuberculosis lesions in other areas should be carefully searched before and during treatment. During treatment, attention should be paid to improving the patient’s health condition, paying attention to rest and increasing nutrition. Chemotherapeutic drugs are detailed in other chapters and will not be repeated here for a course of about 1 year. (B) Topical drug therapy 1, local topical anti-tuberculosis drugs: a variety of anti-tuberculosis drugs formulated into different levels of ointment, cream rubbed on the lesions, anti-inflammatory, bactericidal, antibacterial, promote the absorption of lesion tissue and healing the role of the wound. Commonly used preparations are 5% isoniazid ointment, 15%-20% para-aminosalicylic acid ointment, 10% streptomycin ointment, 10% gentamicin ointment, 1% kanamycin ointment, 10% cod liver oil ointment, 0.025%-0.1% retinoic acid ointment, applied 2-4 times a day. 2, topical caustic drugs: can be used 2% caustic gallbladder ointment, painless phenol liquid, (crystal phenol 50.0g, dacronin 1.0% g, camphor 0.6g, anhydrous alcohol 5.0g, glycerin 5.0g), on tuberculosis lesion tissue has a destructive effect, first from 5%, gradually increase the concentration. Pure carbolic acid, 30%-60% trichloroacetic acid solution and 50% lactic acid solution can also be applied to the proliferative skin damage for corrosion and cauterization to destroy the lupus nodules and eliminate the damage, and after the scabs fall off, the treatment can be repeated according to the lesions. 3. Local lesion injection: Isoniazid plus lidocaine is used for injection around the lesion, and streptomycin 0.5-1.0g plus 1% procaine 5-10ml is also commonly used. 10mg of desoximetasone acetate can be added according to the condition and injected into the base of the lesion and its surrounding area once a week for 6 times. Isoniazid, butylamine kanamycin and 10% wolfsbane solution can also be used for local treatment. 4.Physical therapy: X-ray irradiation can promote the absorption of tuberculosis tissue, flatten the proliferating and thickening skin lesions, and soften the scar. Ultraviolet irradiation can promote local blood circulation of lesions, enhance patients’ resistance and reduce susceptibility to tuberculosis bacteria. In addition, electrocoagulation, cryotherapy and laser therapy are used to destroy tuberculosis tissue by freezing or high temperature, while promoting tissue healing. 5.Surgical excision: surgical excision is suitable for early small isolated damage, such as lupus vulgaris, warty skin tuberculosis, scrofulous skin tuberculosis involving lymph nodes and fistulas, and the excision should be slightly larger than the lesions and have sufficient depth to avoid recurrence.