Necrobiosis Lipoidica

Necrobiosis lipoidica (NL) is an inflammatory skin disorder characterized by irregularly shaped, callous lesions with reddish-brown pigmentation and central atrophy. It was originally described in conjunction with diabetes - in 1929, by Oppehheim who coined the name dermatitis atrophicans lipoidica diabetica and, in 1932, by Urbach who called it necrobiosis lipoidica diabetica. Today the term is applied to all cases, whether occurring in diabetics or not. NL has also been reported in association with inflammatory bowel disease, granuloma annulare and sarcoid.

The pathology is collagen degeneration with granulomatous response, associated with thickened blood vessels and fat deposition. Underlying cause is unknown: aetiology has suggested to be an antibody-mediated vasculitis with secondary collagen degeneration or diabetic microangiopathy.

NL is a rare skin condition. Whilst there is a high prevalence of diabetes mellitus in patients with NL (50% NL occurs in diabetics), the reported prevalence of NL in diabetic patients is less than 1%.¹ It most commonly presents in the 30s but can present at any age including infancy. It tends to appear earlier in diabetics than in others: in one study, approximately 2% young diabetics (aged up to 22 years)had a NL lesion compared to none of the control subjects.² It is 3 times as common in women as in men. Non-diabetic familial clustering of NL does occur but extremely rarely.³
Smoking is more prevalent in diabetic patients with NL than without, as are diabetic complications (retinopathy and nephropathy) although the presence of NL does not correlate with diabetic control.⁴

• Shiny patches slowly enlarge over months or years. They are initially a reddish brown and 1 to 3mm in diameter but progress to yellow and become depressed and atrophic plaques.
• The commonest site is the pretibial area but they can occur on the face, scalp, trunk and upper arms where they are less likely to be correctly diagnosed.
• In about ¾ of cases there is no pain (due to associated neuropathy), but they may be very painful.
• Trauma produces ulceration.
• They may display the Koebner phenomenon in which lesions occur in areas of trauma. This typically occurs with psoriasis and lichen planus.

Usually the appearance is fairly typical but variations can be difficult to diagnose. Consider as a cause of atypical leg ulcers in diabetic patients.⁵

• Superficial annular lesions may look like granuloma annulare
• Yellow, fatty lesions may resemble xanthoma
• Sarcoidosis can appear very similar, even on histology
• Rheumatoid nodules are similar histologically but tend to be raised rather than atrophic. Ulcerated necrobiotic areas have been described in rheumatoid arthritis
• Varicose eczema produces a scaly rash and is usually near the malleoli.

If the patient is not known to be diabetic this must be checked. Biopsy of the lesion may be helpful but beware of poor wound healing.

Management is impaired by lack of understanding of the aetiology of the condition. No treatment to date is completely effective, and whilst numerous treatments have been tried, none has proven effectiveness based on controlled trials.

• Trauma should be avoided.
• Traditionally, the mainstream view has been that improving diabetic control is not beneficial to NL lesions but this has been challenged¹ and tight diabetic control may reduce the incidence of this rare disease and possibly aid healing. Since smoking is commoner in affected adults, it would seem wise to counsel against it. Use of glitazones has benefitted NL lesions in some cases.⁶
• Topical or intralesional steroids may reduce inflammation but it does not benefit burned out lesions and may aggravate atrophy. Courses of systemic corticosteroids have also been used but are controversial, not least since they may upset glycaemic control.⁷
• Anti-platelet treatment seems logical but controlled trials have had different results. Aspirin and dipyridamole have been used.⁸ Pentoxifylline decreases blood viscosity and increases fibrinolysis and erythrocyte deformity and it may be helpful.⁹ Ticlodipine and perilesional injections of heparin have been used in uncontrolled trials.
• Excision and skin grafting may work but poor blood supply may cause the graft to fail.
• Phototherapy (UVA1) has been as an adjunct to other forms of treatment.¹⁰
• Immunomodulating drugs have also been used to treat NL: cyclosporin¹¹, topical tacrolimus¹² and anti-TNFα therapies¹³ with varying levels of success. Interestingly, a case study describes spontaneous healing of NL following pancreas and kidney transplantation and the immunosuppressive regime is thought to have played a significant role in this improvement.¹⁴

The lesions do not heal well and are usually considered a chronic, relapsing condition. They are known to spontaneously remit and even resolve. Spontaneous remission with residual scars and atrophy was observed in 17% of patients¹⁵ but flare ups are to be expected. Occasionally squamous cell carcinoma can arise in areas of longstanding NL.¹⁶