• Diabetic neuropathic ulcers (mal perforans) are a major complication of diabetes mellitus. Other factors, such as mechanical changes in conformation of the bony architecture of the foot and atherosclerotic peripheral arterial disease, may be contributing causes.

Lesions most often occur at sites of pressure (e.g., the heel), particularly in areas of poor sensory function and poor circulation (Fig. 34.4).

• Ulcers are usually painless as a result of peripheral neuropathy.

• Diabetic neuropathic ulcers should be distinguished from infections and other ulcerations and cutaneous neoplasms that may present as ulcers.

• The diagnosis of many of these entities is generally based upon clinical findings.

• A skin biopsy may be necessary to confirm the diagnosis.

• Acanthosis nigricans (Fig. 34.5) sometimes occurs in insulin-resistant diabetes (also see Figs. 23.19 and 23.20).

• Cutaneous candidiasis may also occur (see Figs. 18.17-18.22)

• Eruptive xanthomas are seen as skin markers for various primary genetic disorders such as certain types of hyperlipidemias or secondary to diabetes (see discussion later in this chapter).

• Diabetic dermopathy is characterized by small brownish, atrophic, scarred, hyperpigmented plaques (Fig. 34.6).

  • Lesions occur primarily on the anterior lower legs in patients with type 1 and type 2 diabetes.

  • It is typically a late manifestation of diabetes and is usually asymptomatic.

  • Diabetic dermopathy must be differentiated from lesions caused by trauma.

• Perforating folliculitis (Kyrle disease) consists of firm, rough, hyperkeratotic papules, which are often hyperpigmented in dark-skinned people.

  • There is a high incidence of perforating folliculitis in patients with long-standing diabetes who are undergoing long-term hemodialysis.

  • Lesions are found most commonly on the extensor surfaces of the extremities. Itching can be intense.

• Disseminated granuloma annulare consists of annular dermal papules (see Chapter 15: InflAMmatory Eruptions of Unknown Cause) that occur both in patients with clinical diabetes and sometimes in individuals with only abnormal glucose levels.

• Scleredema of Buschke-Löwenstein is a rare manifestation of diabetes mellitus. The lesion is a sclerotic, thickened plaque characteristically seen on the upper back.

• Serum glucose levels and glycosylated hemoglobin A1C are determined to confirm the diagnosis of diabetes mellitus.

• Skin biopsies of lesions of necrobiosis lipoidica and granuloma annulare demonstrate palisading granulomas with degeneration of collagen.

• Skin biopsy of perforating folliculitis demonstrates basophilic material in the dermis, with transepidermal elimination.

• Skin biopsies of diabetic dermopathy show thickening of blood vessels and mild perivascular infiltrate.

• Diabetic bullous lesions have subepidermal blistering on hematoxylin and eosin staining of skin biopsy tissue; direct immunofluorescence of skin biopsies in these lesions is negative for immunoglobulins.