NECROBIOSIS LIPOIDICA
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.
