Necrobiotic xanthogranuloma (NXG) is a rare, chronic skin condition classified as a non-Langerhans cell histiocytosis. It is a granulomatous disorder, involving an accumulation of immune cells that form nodules or plaques in the skin. First described in 1980, NXG is recognized as a multisystem disorder, often affecting areas beyond the skin.
The condition progresses over time and typically does not resolve on its own. Its systemic nature means other organs can be involved, necessitating thorough evaluation for individuals diagnosed with NXG.
What is Necrobiotic Xanthogranuloma?
Necrobiotic xanthogranuloma typically manifests as firm, yellow-to-orange or reddish-brown plaques and nodules on the skin. These lesions vary in size, from 0.3 cm to 25 cm, and may ulcerate or scar over time.
These characteristic lesions are most commonly found around the eyes, affecting the periorbital region in over 80% of cases. They can also appear on the trunk, limbs, and other body areas. The term “necrobiotic” refers to the degeneration of collagen fibers within the skin, while “xanthogranuloma” describes the presence of lipid-laden immune cells, or foamy histiocytes, that accumulate in these areas.
Underlying Medical Associations
Necrobiotic xanthogranuloma has a strong association with underlying monoclonal gammopathy, particularly IgG monoclonal gammopathy of undetermined significance (MGUS). This involves an abnormal IgG protein (M-protein) in the blood, found in almost all patients with NXG and monoclonal gammopathy.
The skin lesions of NXG can sometimes appear before the diagnosis of the underlying blood disorder. Patients may later develop multiple myeloma or other lymphoproliferative disorders, such as small lymphocytic lymphoma or B-cell chronic lymphocytic leukemia. Therefore, ongoing surveillance for these hematological conditions is important for individuals with NXG.
Diagnosis and Evaluation
A skin biopsy is necessary for a definitive diagnosis of necrobiotic xanthogranuloma. Pathologists examine the tissue microscopically for specific features. These include palisading granulomas, which are clusters of immune cells arranged in a fence-like pattern, surrounding areas of degenerating collagen (necrobiosis).
The biopsy may also reveal foamy histiocytes (lipid-filled immune cells), Touton giant cells, foreign body giant cells, and cholesterol clefts. Beyond the skin biopsy, a comprehensive systemic workup is performed, including blood tests like serum protein electrophoresis (SPEP) and immunofixation electrophoresis (IFE), to screen for associated monoclonal gammopathy.
Treatment Options
Treatment for necrobiotic xanthogranuloma is challenging due to its rarity and lack of universally agreed-upon guidelines. The aim is to manage symptoms and prevent lesion progression. Treatment approaches often include topical corticosteroids, applied directly to the skin or injected into lesions.
Systemic therapies may also be used. These include oral corticosteroids, immunosuppressants such as azathioprine, cyclophosphamide, or methotrexate, and sometimes chemotherapy agents like chlorambucil or melphalan, especially if an underlying blood disorder is present. Addressing the underlying monoclonal gammopathy with appropriate therapy is often a significant factor in improving skin lesions.
Living with Necrobiotic Xanthogranuloma
Necrobiotic xanthogranuloma is a chronic condition with a slowly progressive and often relapsing course. Consistent monitoring of skin lesions and any associated systemic conditions is important. While the prognosis is generally favorable, the disease can lead to complications.
Potential complications include ulceration of skin lesions, secondary infections, and visual impairment if lesions affect the eyes and surrounding structures. A multidisciplinary approach involving dermatologists, hematologists, and ophthalmologists is often beneficial for managing the condition and maintaining a good quality of life.