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Necrobiosis Lipoidica Diabeticorum
Necrobiosis lipoidica diabeticorum characteristically involves the legs. Its histologic manifestations depend in
part on the stage of the disease at the time of biopsy. The palisaded granuloma of necrobiosis lipoidica diabeticorum (NLD) is a process which usually affects the reticular dermis in a diffuse pattern; the focal
nature of the lesions of granuloma annulare (GA) generally is not a feature of NLD. A lesion of NLD likely will involve the entire reticular dermis of a diagnostic biopsy specimen and even may extend along septa
into the subcutaneous tissue (the process, in its distribution as seen on a single specimen, tends to be, at least, pan-dermal in the reticular dermis).
Early on, the changes in a lesion of NLD may be mild (S9C26P17-8). Some examples are relatively free of inflammatory infiltrates (S9C27P18-4).
Characteristically, the inflammatory infiltrates of a lesion of NLD have a layered appearance (S9C25bP16b-1, S9C26P17-1 & 2, S9C27P18-1 & 2, S9C29P20-1-3, & S9C29aP20a-1 & 2);
this multlayering is produced, in large part, by the prominence of perivascular cuffs of inflammatory cells along the venous plexus of the reticular dermis. In addition, the infiltrates tend to be band-like at the
interfaces between the lesion and the papillary dermis (superiorly) and the subcutaneous fat (inferiorly). Finally, the infiltrates tend to be interstitial, they form traceries and palisades at the margins of
zones of necrosis and areas of degeneration, or fibrosis in the reticular dermis. The infiltrates of NLD tend to be more strikingly granulomatous than those of GA. Histiocytic giant cells may be a prominent feature (S9C25bP16b-2). In the zones of degeneration and necrosis, there is a reduction, or absence, of connective tissue cells. Typically, in the areas
of fibrosis, collagen bundles are streaked in a direction which parallels the surface of the skin. Rare examples show focal areas of basophilic necrosis (S9C29aP20a-1-4)
In lesions of NLD, fibrin deposits are common among the altered collagen bundles (S9C25bP16b-3). Vessels of the skin in lesions of NLD tend to have thickened, hyalinized walls with narrowed lumens (arteriolosclerosis) (S9C28P19-5). Some of the small vessels with narrowed lumens have thickened walls that are loosely laminated (S9C28P19-6). Small vessels within, and at the margins, of lesions of NLD commonly show thrombosis and fibrinoid necrosis (S9C25bP16b-4, & S9C28P19-4). Muscular vessels of the subcutaneous tissue
may show lymphocytic infiltrates, or even granulomatous changes (S9C28P19-2 & 3). Small muscular vessels of the dermis also can show
granulomatous changes.
In some examples, the collagen bundles are coarsened. In addition, they appear to be streaked in a direction
that parallels the surface of the skin (S9C26P17-1-4, S9C27P18-1, 3 & 4, S9C28P19-1, 7 & 8, S9C29P20-1-3, S9C29aP20a-1-3). Focally, the dermis may be hyalinized (S9C26P17-6). In areas, elastic fibers are reduced in number. In some examples, the collagen bundles focally are replaced by a loosely laminated,
fibrous matrix which is more richly cellular than the neighboring portion of the lesion.
The perivascular infiltrates commonly have a granulomatous quality, but may be mostly lymphoid in character. In
contrast to granuloma annulare, the perivascular infiltrates commonly contain plasma cells (S9C26P17-9, & S9C29aP20a-7 & 8).
Skin appendages may be interrupted by the areas of necrobiosis (S9C26P17-7, & S9C28P19-7). Where the interrupted skin appendages abut upon the
altered dermis, the epithelium often is hyperplastic in a pattern of pseudoepitheliomatous hyperplasia. In the areas of pseudoepitheliomatous hyperplasia, epithelium, of skin appendage origin, may extend in
plate-like patterns at the interface between viable and necrotic connective tissue.
Lowitt MH, Dover JS: Necrobiosis lipoidica. J Am Acad Dermatol 1991;25: 735-48.
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