Pigmentary urticaria (urticaria pigmentosa) is a mast cell disorder characterized by round or oval pigmented spots or pigmented nodules that become red and swollen upon scratching or friction. It often begins in early childhood. In 1969, Nettie Ship first described the skin manifestations of this condition, referring to it as chronic urticaria with residual brown spots. Unna noted the relationship between this disease and mast cells, while Ellis was the first to report that mast cell infiltration could occur not only in the skin but also in other organs such as the liver, spleen, bone marrow, and lymph nodes. The condition typically follows a benign course, and skin lesions in children may resolve spontaneously. In adults, the lesions rarely disappear. A minority of patients with systemic involvement may experience a chronic progressive course, and very few cases may undergo malignant transformation, though most remain benign.

bubble_chart Etiology

The cause of the disease is unknown, but the presence of numerous mast cells in the skin lesions suggests it is a mast cell tumor. Many mast cells may also be found in the liver, spleen, lymph nodes, and bone marrow of patients, classifying it as one of the reticular endothelial granulomatous diseases. The excessive concentration of mast cells in the skin may be congenital, and factors such as smallpox vaccination, tetanus antitoxin injections, chickenpox or measles infections, or even psychological stress can trigger the manifestation of this congenital disorder. Skin pigmentation results from melanin hyperplasia, while patches and nodules are caused by the massive aggregation of mast cells. The Lewis triple response demonstrates that rubbing the affected area can induce mast cells to release substances like histamine, affecting capillary dilation and permeability, leading to the formation of localized wheal rashes. Since the disease is more prevalent in certain ethnic groups and familial cases are observed—with one parent and one or two children often affected—it is considered to be inherited recessively.

All types are characterized by clusters of mast cells occurring in the superficial dermis between collagen fibers, and they may also appear around blood vessels, hair follicles, sweat glands, and within tissue spaces. The granules of mast cells are composed of mucopolysaccharides and exhibit metachromasia with Giemsa and toluidine blue staining. If the granules are lost, the mast cells become difficult to identify.

In the lesions of pigmented macules, there is sparse infiltration of mast cells in the upper dermis, mainly distributed around blood vessels. The mast cells have spindle-shaped nuclei, resembling fibroblasts, and are accompanied by nucleated eosinophilic cytoplasm. A few eosinophils may be seen, with increased melanin in the epidermal basal layer above. In nodular lesions, the entire dermis shows dense, tumor-like infiltration of mast cells, often with prominent granules.

In diffuse lesions, mast cells may be seen infiltrating in a band-like pattern, while in systemic lesions, mast cell infiltration can be observed in systemic tissues.

bubble_chart Clinical Manifestations

Common in children, it often occurs between 3 to 9 months after birth, but some cases are present at birth. It does not affect the child's growth and development, but may involve visceral damage such as hepatosplenomegaly and ascites. The initial lesions are often transient urticaria, which later recur and disappear in the same location. Eventually, they become persistent brownish patches or uneven pigmented nodules. A few patients may develop blisters on the skin lesions, and wheals may appear after scratching, which is a characteristic feature of this disease. The lesions often appear in batches, varying in size, typically from pea to broad bean size, and their number is also variable—ranging from a few to widespread across the body. Some may cause mild itching and lymphadenopathy. In a minority of cases, the rash appears in adulthood and may persist indefinitely. Therefore, some scholars classify it into the following types:

（1）Cutaneous type — Diffuse cutaneous mastocytosis.

（2）Systemic type — Involvement of skin, bones, liver, spleen, and gastrointestinal tract.

（3）Visceral type — Damage to the spleen, bones, and gastrointestinal tract.

2. Malignant — Leukemic nature of the disease.

bubble_chart Diagnosis

Typical cases are not difficult to diagnose, and the formation of wheals in pigmented skin lesions (Darier's sign) has diagnostic value.

bubble_chart Treatment Measures

In addition to the adult type, patients generally recover naturally during adolescence. Disodium cromoglycate is taken orally at 20mg, four times a day, which stabilizes mast cell membranes. Flufenamic acid is taken orally at 0.2g, three times a day, and has an anti-SRS-A effect. Antihistamines and corticosteroids can temporarily relieve itching, while reserpine can alleviate symptoms, control urticaria, and reduce itching.

bubble_chart Differentiation

Pigmented macules and papules should be differentiated from nevi; papules and nodular lesions should be distinguished from juvenile xanthogranuloma and xanthoma. Additionally, differentiation should be made from drug rash, post-inflammatory hyperpigmentation, and melanosis. Local irritation such as scratching can induce a wheal reaction in the lesions of this disease, and the presence of mast cell infiltration in histopathology confirms the diagnosis.