Diagnosis: Necrobiosis lipoidica diabeticorum
Necrobiosis lipoidica diabeticorum (NLD) is a disorder involving subcutaneous collagen degeneration that results in thickening of blood vessel walls, fat deposition, and the formation of granulomas. It affects up to 1.2% of all patients with type 1 and type 2 diabetes, and occurs in patients without diabetes, although it is less common.1 NLD mostly affects females, with a ratio of 3:1.2 It’s also been described in patients with rheumatoid arthritis, in whom lesions are mostly ulcerated.3
The lesions typically start as multiple shiny, painless, red-brown patches that tend to appear in the lower extremities and slowly coalesce and enlarge over months to years, forming yellow atrophic plaques. The thin overlying epidermis contains many telangiectatic vessels.4 In rare cases, chronic lesions have developed into squamous cell carcinomas.5
A diagnosis is established based on the appearance of the rash and a suggestive history—as was the case with our patient. Lab tests generally aren’t required, but should be performed to check for diabetes (if a diagnosis has not been established) and to explore relevant differential diagnoses.
The differential Dx includes granuloma annulare
In its early stages, the superficial annular lesions of NLD closely resemble granuloma annulare, which is characterized by violaceous or skin-colored annular rings with firm papules or nodules. Skin manifestations of sarcoidosis may also resemble the condition, but associated systemic manifestations help distinguish the two. Rarely, paraproteinemias can develop similar lesions (known as necrobiotic xanthogranuloma) that are associated with elevated blood levels of paraproteins.
The cause
The exact etiology of NLD is not known but a number of factors have been implicated, including microangiopathy, local trauma, metabolic changes (eg, glycoprotein deposition in the vascular endothelium, increased platelet aggregation), and immune-mediated deposition of immunoglobulins and fibrinogen in the vascular walls.6
The histologic picture reveals layers of subcutaneous and intradermal interstitial and palisade granulomas. These granulomas are made up of histiocytes and sometimes eosinophils. Surrounding areas show significant degeneration of collagen and nerve endings. Hence, the lesions are generally painless. Surface trauma to the lesions creates ulcerations that occasionally lead to pain. Vasculitic involvement of the traumatic plaque may demonstrate Koebner phenomenon.7
No correlation. NLD does not correlate with glycemic control or with the presence or progression of vascular (or other) complications of diabetes.8 It can, however, be a clue to the presence of diabetes.