Certain cutaneous disorders appear to be specific for DM (for example, diabetic thick skin), whereas others are present in the general population but are more frequent in diabetic individuals.
Diabetic dermopathy is the most common skin disorder associated with DM. It is quite frequent and presents at a rate, according to various authors, ranging up to 50 percent in diabetic patients, but only 3 percent in the general population. It is more prevalent in men older than 50 years of age, with long-standing DM. It is characterized by well circumscribed, brownish, atrophic, round or oval macules and scars, 0.5 to 2 cm in diameter (Figure 18.1). Usually these are located on the extensor surfaces of the shin bilaterally (hence the use of the term shin spots in this situation). They are asymptomatic and usually resolve in 1-2 years, but often relapse in other regions of the shins. There is no special treatment. The cause of the disorder is attributed to microangiopathic changes of the skin vessels.
Necrobiosis lipoidica diabeticorum is a rare dermatosis, with prevalence roughly around 0.3 percent among diabetic patients. Its name emanates from the characteristic necrobiosis, that is the degeneration of collagen in the dermis, the yellow colour of most lesions (due to carotene and lipid deposition) and its association with DM. It is characterized by asymptomatic, red, red-brown or violet plaques on the skin that often enlarge and become yellow centrally. Furthermore, there is atrophy of the epidermis that leads to shiny, transparent skin and visualization of the underlying dermal and subcutaneous vessels (Figure 18.2). The most
Diabetes in Clinical Practice: Questions and Answers from Case Studies. Nicholas Katsilambros et al. © 2006 John Wiley & Sons, Ltd. ISBN: 0-470-03522-6
frequent location is the shins (90 percent), but it can also present on the scalp, face or hands. The plaques may eventually ulcerate, become painful and predispose to infection. There is no satisfactory treatment. Improvement of hyperglycaemia does not result in corresponding improvement of the dermal lesions. Topical corticosteroids have been tried (either applied locally or by intralesional injection), as well as anticoagulants and antiplatelet agents (heparin, aspirin, dipyridamole) and immunosuppressants (cyclosporin, mycophenolate mofetil), without particular success. In a relatively small study, positive results were reported with the use of ultraviolet radiation (PUVA) and topical application of methoxypsoralen. In more infrequent cases, excision and grafting of the skin may even be needed.
The diabetic bullae (bullosis diabeticorum) are an uncommon dermal manifestation of DM. They occur more frequently in men as tense blisters containing clear liquid, more often on the dorsal and lateral surfaces of the hands and feet, on a normal, non-inflammatory base. They are usually asymptomatic and disappear within a few weeks. They do not usually require particular treatment (except perhaps for drainage when they are big in size [Figure 18.3] and local application of antibiotics if there is suspicion of superinfection). Their aetiology is unknown.
Periungual telangiectasia, that is the dilatation of capillaries and venules in the nail folds, is more frequent i n DM (up to 50 percent in diabetics compared to 10 percent in the non-diabetics). The nail-fold capillary loops are examined easily through a magnifying lens and have
been used for functional studies of diabetic microangiopathy, because they are thought to represent the general status of the microcirculation in DM.
The skin of diabetic individuals is often thicker than in non-diabetics, and less elastic. In certain cases this thickness of the skin is pronounced and can potentially lead to scleroedema of the skin, with more frequent localization at the posterior surface of the neck and upper back. Seldom does it extend to the face, arms and abdomen. Scleroedema affects roughly 2.5 percent of Type 2 diabetic patients and is related to obesity and poor diabetes control. In certain cases the combination of skin thickness together with involvement of the small and large joints of the hands leads to cheiroarthropathy, with the inability to approximate the palmar surfaces of the hands (see also Chapter 20: 'Musculoskeletal system and diabetes', and Figure 20.1).
Carpal tunnel syndrome and Dupuytren contracture are also more common in DM.
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