Necrobiosis lipoidica is a rash that is frequently encountered in the dermatology clinic. It is most commonly seen in association with diabetes and is referred to as necrobiosis lipoidica diabeticorum. However, not all cases are seen in conjunction with diabetes mellitus, and the name necrobiosis lipoidica is a more inclusive designation. Patients who present with necrobiosis lipoidica should all be evaluated for underlying diabetes and screened periodically over their lifetime, because 60% to 80% will have or develop some form of glucose intolerance. Necrobiosis lipoidica has been reported to appear any place on the skin, but it is most frequently encountered on the anterior lower extremities. It has a characteristic clinical appearance, and the diagnosis can often be made on clinical grounds alone, without the use of a skin biopsy. The histologic findings are diagnostic of necrobiosis lipoidica. A punch or excisional biopsy is required for diagnosis, because a shave biopsy does not allow for proper histological evaluation of this condition.
Clinical Findings: There appears to be no sexual or racial predilection, and the disease is most commonly diagnosed in early adulthood. In most instances, necrobiosis lipoidica occurs on the anterior lower extremities. The rash typically begins as a tiny red papule that slowly expands outward and leaves behind a depressed, atrophic center with a slightly elevated rim. The borders are very distinct. They are slightly elevated and have a more inflammatory red appearance. They are well demarcated from the surrounding normalappearing skin. The lesions have a broad range of sizes, from a few millimeters in some cases to affecting the entire aspect of the anterior lower legs. The plaques have a characteristic orange-brown coloration and significant atrophy. The underlying dermis appears to be thinned dramatically; the dermal and subcutaneous veins can easily be seen and appear to be popping out of the skin. When palpated, the center of the lesions feel as if there is no dermal tissue present at all. The difference between palpation of the normal skin and palpation of affected skin is striking.
A small percentage of patients experience ulcerations that can be slow and difficult to heal. Rarely, transformation of chronic ulcerative necrobiosis lipoidica into squamous cell carcinoma has been reported. This transformation is more likely to be a result of the chronic ulceration and inflammation than the underlying necrobiosis lipoidica. There are no other associations with necrobiosis lipoidica except for diabetes.
Pathogenesis: The pathomechanism of necrobiosis lipoidica is unknown. Theories have been suggested, but no good scientific evidence has pinpointed the cause.
Histology: The histology of necrobiosis lipoidica is characteristic. A punch or excisional biopsy is needed to ensure a full-thickness specimen. There is a “cake layering” appearance to the dermis, with necrobiotic collagen bundles within palisaded granulomas alternating with areas of histiocytes and multinucleated giant cells of both the foreign body and the Langhans type. The differential diagnosis histologically is between granuloma annulare and necrobiosis lipoidica. In necrobiosis lipoidica, the inflammatory infiltrate contains less mucin and more plasma cells. The inflammation in necrobiosis lipoidica also tends to extend into the subcutaneous adipose tissue.
Treatment: Treatment is typically initiated with the use of high-potency topical steroids. It may seem counterintuitive to treat an atrophic condition with topical corticosteroid creams, which can cause atrophy. In cases of necrobiosis lipoidica, however, the high-potency steroid agents do not lead to an increase in the atrophy. The steroid agents act to decrease and stop the inflammatory infiltrate from occurring and perpetuating itself. Intralesional injections of triamcinolone have also been successful. Many other agents have been anecdotally reported to be successful in treating this condition, although they have not been tried in standardized, placebo-controlled studies. Gaining control of the underlying diabetes does not seem to play a role in the outcome of the skin disease. Ulcerations should be treated with aggressive wound care, and compression garments should be worn if edema or venous insufficiency is present. Ulcers may take months to heal. Once the inflammation has been stopped, most people have residual atrophy that may be permanent or may improve slightly with time.