A New Appraisal of Dermatologic Manifestations of Diabetes Mellitus

Diabetes mellitus is a morbid and costly condition that carries a high burden of disease for patients (both with and without a diagnosis) and for society as a whole. The economic burden of diabetes in the United States recently was estimated at nearly $250 billion annually,¹ and this number continues to rise. The cutaneous manifestations of diabetes are diverse and far-reaching, ranging from benign cosmetic concerns to severe dermatologic conditions. Given the wide range of etiology for diabetes mellitus and its existence on a spectrum of severity, it is perhaps not surprising that some of these entities are the subject of debate (vis-à-vis the strength of association between these skin conditions and diabetes) and can manifest in different forms. However, it is clear that the cutaneous manifestations of diabetes are equally as important to consider and manage as the systemic complications of the disease. In analyzing associations with diabetes, it is important to note that given such a high incidence of diabetes among the general population and its close association with other disease states, such as the metabolic syndrome, studies aimed at determining direct relationships to this entity must be well controlled for confounding factors, which may not even always be possible. Regardless, it is important for dermatologists and dermatology residents to recognize and understand the protean cutaneous manifestations of diabetes mellitus, and this column will explore skin findings that are characteristic of diabetes (Table 1) as well as other dermatoses with a reported but less clear association with diabetes (Table 2).

Skin Findings Characteristic of Diabetes

Diabetic Thick Skin

The association between diabetes and thick skin is well described as either a mobility-limiting affliction of the joints of the hands (cheiroarthropathy) or as an asymptomatic thickening of the skin. It has been estimated that 8% to 36% of patients with insulin-dependent diabetes develop some form of skin thickening²; one series also found this association to be true for patients with non–insulin-dependent diabetes mellitus (NIDDM).³ Skin thickening is readily observable on clinical presentation or ultrasonography, with increasing thickness in many cases associated with long-term disease progression. This increasing thickness was shown histopathologically to be a direct result of activated fibroblasts and increased collagen polymerization, with some similar features to progressive systemic sclerosis.⁴ Interestingly, even clinically normal skin showed some degree of fibroblast activation in diabetic patients, but collagen fibers in each case were smaller in diameter than those found in progressive systemic sclerosis. This finding clearly has implications on quality of life, as a lack of hand mobility due to the cheiroarthropathy can be severely disabling. Underlining the need for strict glycemic control, it has been suggested that tight control of blood sugar levels can lead to improvement in diabetic thick skin; however, reports of improvement are based on a small sample population.⁵ Huntley papules are localized to areas on the dorsum of the hands overlying the joints, demonstrating hyperkeratosis and enlarged dermal papillae.⁶ They also can be found in a minority of patients without diabetes. Interestingly, diabetic thick skin also has been associated with neurologic disorders in diabetes.⁷ Diabetic thick skin was found to be significantly (P<.05) correlated with diabetic neuropathy, independent of duration of diabetes, age, or glycosylated hemoglobin levels, though no causal or etiologic link between these entities has been proven.

Yellow Nails

Nail changes are well described in diabetes, ranging from periungual telangiectases to complications from infections, such as paronychia; however, a well-recognized finding, especially in elderly diabetic patients, is a characteristic yellowing of the nails, reported to affect up to 40% of patients with diabetes.⁸ The mechanism behind it likely includes accumulation of glycation end products, which also has been thought to lead to yellowing of the skin, and vascular impairment.⁹ These nails tend to exhibit slow growth, likely resulting from a nail matrix that is poorly supplied with blood, and also can be more curved than normal with longitudinal ridges (onychorrhexis).¹⁰ It is important, however, not to attribute yellow nails to diabetes without considering other causes of yellow nails, such as onychomycosis, yellow nail syndrome, and yellow nails associated with lymphedema or respiratory tract disease (eg, pleural effusion, bronchiectasis).¹¹

Diabetic Dermopathy

Colloquially known as shin spots, diabetic dermopathy is perhaps the most common skin finding in this patient population, though it also can occur in up to 1 in 5 individuals without diabetes.¹² Although it is very common, it is not a condition that should be overlooked, as numerous studies have shown an increase in microangiopathic complications such as retinopathy in patients with diabetic dermopathy.^13,14 Although follow-up studies may be necessary to fully characterize the relationship between shin spots and diabetes, it certainly is reasonable to be more wary of diabetic patients presenting with many shin spots, as the general consensus is that these areas represent postinflammatory hyperpigmentation and cutaneous atrophy in the setting of poor vascular supply, which should prompt analysis of other areas that might be affected by poor vasculature, such as an ophthalmologic examination. Antecedent and perhaps unnoticed trauma has been implicated given a possible underlying neuropathy, but this theory has not been supported by studies.