Yellow skin tumor diseases (cutaneous xanthomatosis) refer to a group of conditions characterized by localized accumulation of lipid-laden histiocytes in the dermis, clinically presenting as yellow patches, papules, or nodules. These conditions are often associated with elevated lipid levels and abnormalities in other organs.

bubble_chart Etiology

Xanthomas are commonly seen in conditions characterized by decreased triglyceride catabolism, caused by abnormalities in lipoprotein lipase activity, impaired hepatic remnant catabolism, or abnormal low-density lipoprotein (LDL) breakdown, including various primary and secondary sexually transmitted diseases.

Clinically, xanthomas are classified into two main categories: primary xanthomas and secondary xanthomas. Primary xanthomas can be further divided into familial and non-familial types. Familial xanthomas have genetic inheritance, varying degrees of lipid metabolism disorders, and systemic manifestations, known as primary familial hyperlipoproteinemic xanthomas (which can be subdivided into types I, II, III, IV, and V hyperlipoproteinemia). Non-familial cases are sporadic, with disease causes still unclear, often presenting with normal blood lipids, and are referred to as primary non-familial normolipidemic xanthoma diseases. Secondary xanthomas refer to those caused by other diseases leading to lipid metabolism disorders and elevated blood lipids, such as diabetes, myeloma, and lymphoma. Secondary xanthomas can also occur in diseases without elevated blood lipids, such as histiocytosis X, disseminated xanthoma, and juvenile xanthogranuloma.

bubble_chart Pathological Changes

The histopathology of various types of xanthomas is similar. The main feature is the presence of scattered or clustered foam cells in the dermis. These foam cells are histiocytes with phagocytic ability, which, after engulfing large amounts of lipids, become filled with lipid droplets in their cytoplasm. In routine sections, the cytoplasm appears reticulated or foamy because the lipids are dissolved during processing. The nuclei of xanthoma cells are usually single but can also be multiple. The nuclei of multinucleated xanthoma cells are irregularly distributed or arranged in a ring surrounded by foamy cytoplasm. Such multinucleated xanthoma cells are called Touton giant cells. The nests of foam cells are typically surrounded by connective tissue reactions. In older lesions, most foam cells are replaced by fibrosis.

Xanthomas can be classified into different types based on the site of occurrence and appearance:

1. Tuberous xanthoma (xanthoma tuberosum): Commonly occurs on the extensor surfaces of the limbs and areas prone to friction, such as the elbows, knees, finger joints, buttocks, and heels. The lesions appear as yellow or dark brown papules, firm in texture, and may be pedunculated. Over time, the lesions enlarge into nodules, which can reach up to 5 cm in diameter and may coalesce, becoming firmer due to fibrosis. Tuberous xanthoma may coexist with palmar xanthoma or tendinous xanthoma; occasionally, it may also accompany eruptive xanthoma or xanthelasma. Involvement of mucous membranes is rare. Even if blood lipid levels return to normal, the lesions are unlikely to regress. This type primarily occurs in cases with elevated B-lipoproteins, specifically types IIA and III, and occasionally in types IIB and IV.
2. Plane xanthoma (xanthoma planum): This type presents as soft, pale yellow to light brown patches or slightly elevated grade I patches. They may be localized or widespread, with diameters up to 5 cm, and can appear on the eyelids (xanthelasma), head, neck, trunk, and limbs. Lesions may also occur on the palms, palmar creases, and fingertips. Plane xanthomas typically persist and may coexist with tuberous xanthoma or eruptive xanthoma. Approximately 60% of patients have type III hyperlipoproteinemia, while a minority may have type IV. However, cases with normal blood lipoprotein levels have also been reported.
3. Tendinous xanthoma (xanthoma tendinosum): Can involve tendons, ligaments, muscle membranes, and bone membranes, often affecting the back of the hands, fingers, elbows, knees, and heels. The skin presents as painless, firm nodules, about 1 cm or larger, most prominent on the knuckles and Achilles tendon. It may coexist with tuberous xanthoma and xanthelasma. Tendinous xanthoma is seen in types II and III hyperlipoproteinemia, and occasionally in patients with normal blood lipids but suffering from cerebrotendinous xanthomatosis, characterized by white internal visual obstruction, tendon, lung, and cerebellar xanthomatosis. Due to cerebellar involvement, cerebellar ataxia and intellectual decline may occur. There are also reports of tendinous xanthoma in patients with normal blood lipids. Even after correcting lipid abnormalities, tendinous xanthoma may not regress.
4. Eruptive xanthoma (xanthoma eruptivum): Presents as sudden clusters of red or yellow papules, ranging from pinhead to pea-sized, surrounded by erythema, resembling pustules, and accompanied by intense itching, which may lead to ulceration. Lesions often resolve spontaneously and commonly appear on the extensor surfaces of the limbs, particularly the elbows, knees, buttocks, back, abdomen, and pressure areas of the trunk. The face, head, lips, and palate are rarely affected. Oral lesions are usually isolated but may cluster to form patches and may be accompanied by the Koebner phenomenon. Lesions may result from high plasma triglyceride levels and are also seen in patients with types I, III, IV, or V hyperlipoproteinemia. After serum lipid abnormalities resolve, the lesions often disappear without leaving scars, though hypopigmentation may occasionally occur.
5. Xanthelasma: Presents as yellowish-white flat or slightly raised patches, primarily located on the upper eyelids but also seen on the lower eyelids, especially near the inner canthus. Lesions may coalesce and feel soft to the touch. It mainly occurs in adults, though rarely in adolescents and children. About 25% of patients have elevated plasma cholesterol levels. The incidence of hyperlipoproteinemia is higher in individuals who develop xanthelasma during youth.

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bubble_chart Diagnosis

Yellow, orange-yellow patches, papules, or nodules, combined with histopathology, make diagnosis relatively straightforward. Tendon xanthomas should be differentiated from pain wind, thecal cysts, tenosynovial giant cell tumors, and lipoid dermatoarthritis. Eruptive xanthomas should be distinguished from disseminated xanthomas, eruptive syringomas, disseminated granuloma annulare, foxtail millet granulomatous sarcoidosis, and leiomyomas.

bubble_chart Treatment Measures

1. For patients with combined hyperlipoproteinemia, dietary control should be tailored according to different types, providing a low-fat and low-sugar diet. Lipid-lowering medications such as cholestyramine, clofibrate, and nicotinic acid can be administered.
2. For localized, few, and small skin lesions, methods such as electrolysis, electrocoagulation, laser, or liquid nitrogen cryotherapy can be considered for removal. Larger lesions may require surgical excision.