bubble_chart Overview

Skin subcutaneous nodules are the manifestation of subcutaneous nodule disease on the skin. They can be caused by subcutaneous nodule bacteria from systemic lesions spreading through the blood, lymph, or nearby tissues to infect the skin, or by external subcutaneous nodule bacteria directly infecting damaged skin or mucous membranes. The former includes conditions like papulonecrotic subcutaneous nodular rash and erythema induratum, while the latter includes examples such as lupus vulgaris and verrucous skin subcutaneous nodules.

bubble_chart Epidemiology

﹝Complications﹞

﹝Efficacy Evaluation﹞

bubble_chart Etiology

Differential Diagnosis

bubble_chart Clinical Manifestations

(1) Lupus vulgaris commonly occurs in children and young adults. The rash consists of dark red nodules ranging from foxtail millet to soybean size, soft in texture with infiltration, which may enlarge and merge into patches. When pressed with a glass slide, the nodules exhibit an apple-jelly color change, which is a characteristic manifestation. The nodules may ulcerate, forming atrophic scars. It predominantly affects the face, limbs, and buttocks. Subjective symptoms are mild.
(2) Verrucous skin tuberculosis predominantly affects adult males. Initially, it presents as small dark red papules, which gradually enlarge and merge into patches with surface proliferation, and pus may ooze from the crevices. The patches expand outward while the center heals, leaving atrophic scars. It commonly occurs on the dorsum of the hands, feet, and buttocks. Subjective symptoms include cutaneous pruritus. The course is slow and protracted.
(3) Papulonecrotic tuberculid is more common in young adults, especially in spring. It begins as scattered, firm papules ranging from foxtail millet to mung bean size, dark red or purplish-red in color, with central necrosis forming pustules. After ulceration, black crusts form, and upon removal, a crater-like ulcer is revealed, healing over several months to leave depressed scars and pigmentation. The rash may recur in batches, predominantly on the extensor surfaces of the limbs, especially near the elbows and knees. Subjective symptoms are often absent.

(4) Erythema induratum is more common in young women, especially in spring and autumn. It begins as several subcutaneous nodules that gradually enlarge and adhere to the skin, firm and fixed, dark red or bluish-purple, slightly elevated above the skin surface. After several months, they may resolve spontaneously, leaving pigmentation. Alternatively, they may soften and ulcerate, forming undermined ulcers that heal with painful scars. It predominantly affects the flexural aspects of the lower legs. Subjective symptoms include burning pain and mild tenderness.

bubble_chart Prognosis

To prevent subcutaneous nodules, it is essential to actively treat internal subcutaneous nodule lesions and avoid trauma. The main medications for treatment include anti-tuberculosis drugs such as isoniazid, streptomycin, rifampicin, and ethambutol, with emphasis on adequate dosage, regular administration, and full-course therapy. Topical application of 5% isoniazid ointment or 15%-20% sodium para-aminosalicylate ointment is recommended. For small lesions, laser therapy, cryotherapy, electrocautery, or surgical excision may also be performed.