How does prurigo nodosa happen? What are the clinical features? Which diseases should be differentiated from?

The common cause of prurigo nodosa is the bite of mosquitoes, bedbugs or other insects, and some patients are related to mental factors, gastrointestinal dysfunction and endocrine disorders. Such patients may also have genetic qualities. Traditional Chinese medicine calls it "horse scab" and "stubborn dampness accumulation" The clinical features of prurigo nodosa are: 1. Characteristics of skin lesions: at first, it was reddish papules or wheal papules, which quickly evolved into hemispherical nodules and were solid. Due to obvious scratches and keratinization, the surface is rough and warty, brown or dark brown. Severe scraping will cause the surface of nodules to peel off. The course of the disease is very long, and it will not heal for a long time. Pigmentation and mossy changes often occur in affected areas. 2. Common parts: common in limbs, especially the extended side of the calf. The number of nodules varies, and most of them are isolated and scattered. 3. Conscious symptoms: severe itching, causing severe scratching. Common in adult women. 4. Histopathology: The epidermis is obviously hyperkeratinized, the spinous layer is thickened, and the epidermal process is widened and irregularly extended. Perivascular lymphocyte infiltration in superficial dermis. Prurigo nodosa should be differentiated from the following diseases: 1. Primary cutaneous amyloidosis: amyloidosis is a brown flat papule with dense distribution, which is most common in the front of the calf and tibia. Histopathology can be used for differentiation. 2. Hypertrophic lichen planus: Hypertrophic plaque with verrucous hyperplasia, purplish red or purple, with thin scales and scattered papules around it, with specific histopathological changes. 3. Polymorphic solar rash: The rash of upper limbs can be manifested as brown papules and nodules, but the disease mainly occurs in the exposed parts of the sun, rarely involving lower limbs, and the incidence has obvious seasonality. 4. Nodular pemphigoid: It usually occurs on the extended side of trunk and limbs. Nodular lesions precede bullous lesions, and blisters appear on nodules or normal skin. Pathological and immunopathological examination showed special changes of pemphigoid. 5. papular urticaria: it mostly occurs in spring and autumn, and the course of disease is short. The lesions are mainly wheal papules and papules.