Necrobiotic xanthogranuloma is a rare skin condition that is frequently associated with an underlying monoclonal gammopathy. It was first described in the early 1980s. Since then, many cases have been reported that have confirmed this to be a distinct, albeit unusual and infrequently encountered, skin condition. The pathological findings of necrobiotic xanthogranuloma are distinctive and are required to make the diagnosis. Patients with this diagnosis need to be monitored routinely to watch for the development of a monoclonal gammopathy and the possibility of multiple myeloma.
Clinical Findings: So few cases of necrobiotic xanthogranuloma have been reported that no firm conclusion can be made on the epidemiology of the disease. However, it is a disease of older adulthood, with almost all cases occurring after the age of 50 years. The lesions have been reported to occur anywhere on the human body, but they are found most often on the forehead, cheeks, and temporal regions around the eyes. The periorbital region is almost always affected. Necrobiotic xanthogranulomas are typically yellowish to red papules and plaques. There may be intervening atrophy between the areas of involvement. The leading edge of the plaques may have a red or violaceous hue. Occasionally, nodules form. Secondary ulceration is frequently reported, as are telangiectases and dilated dermal vessels, which are most prominent in the regions of atrophy. The ulcerations take an extended period to resolve. Most patients are distraught by the appearance of the rash and complain of a mild pruritus, although many have no symptoms. The clinical differential diagnosis includes forms of planar xanthomas. A skin biopsy helps differentiate these conditions. This disease progresses over time and typically does not spontaneously remit.
Patients almost always complain of dry eyes or have objective findings of proptosis. In rare cases, necrobiotic xanthogranuloma affects the lacrimal gland and retrobulbar fat tissue.
Necrobiotic xanthogranuloma is associated with an immunoglobulin G-κ (IgG:κ) monoclonal gammopathy in most cases. The presence of a gammopathy should make the clinician seek the advice of a hematologist to perform a bone marrow biopsy to help evaluate for multiple myeloma. A small percentage of patients with this gammopathy have or will develop multiple myeloma. Other frequently abnormal laboratory tests in necrobiotic xanthogranuloma include an elevated erythrocyte sedimentation rate (ESR), a decreased level of complement C4, and leukopenia. Many other abnormalities have been described, providing more evidence that this is a systemic disease and not an isolated skin disease. Lesions of necrobiotic xanthogranuloma have also been described to occur in the upper respiratory system and in the heart.
Pathogenesis: The pathogenesis has been theorized to be an antibody response to a self-antigen, most likely a form of lipid. This is unproven, and the exact etiology is unknown.
Histology: The biopsy findings of necrobiotic xanthogranuloma are unique and characteristic. A punch biopsy or excisional biopsy should be performed to allow for adequate evaluation. On first glance, the entire dermis is filled with inflammatory cells. The inflammation is in the granulomatous category. A unique and characteristic finding, when seen, is that of cholesterol-filled, needle-shaped clefts within the granulomatous infiltrate. Giant cells, both the foreign body type and the Touton type, are commonly seen. The granulomatous infiltrate surrounds and envelops necrobiotic collagen tissue. There is usually an underlying, predominantly lobular panniculitis without vasculitis.
Treatment: Therapy is difficult. No randomized prospective studies have been performed on this rare condition, so only anecdotal therapies have been reported. Topical and oral steroids have been somewhat successful. Chemotherapeutic agents have been used with variable success, including the alkylating agents. Results have been varied, with some patients experiencing long-term remission. Patients all need to be screened for gammopathy and for the development of multiple myeloma. The presence of myeloma portends a worse prognosis.