Diabetic dermopathy (shin spots)

Definition

Diabetic dermopathy is one of the most common skin changes in diabetes mellitus. It presents as round to oval, light brown to reddish-brown, slightly depressed (atrophic) patches, typically on the shins ("shin spots").

Occurrence & epidemiology

Up to 30% of people with diabetes are affected, especially older patients or those with diabetes for at least 10–20 years; an association with raised HbA1c has been described. Single lesions also occur without diabetes, particularly after injury; four or more lesions are almost exclusively found in diabetes.

Aetiopathogenesis

The cause is unknown. Dermopathy is associated with the microangiopathic complications retinopathy, neuropathy and nephropathy, and an association with coronary artery disease has also been shown. Because the lesions lie over bony prominences, an exaggerated response to minor trauma is assumed; lesions have been observed after heat, cold or blunt injury.

Clinical features

• Round or oval reddish-brown patches, initially scaly, later flat and depressed.
• Usually on both shins; less often on the front of the thighs, forearm, side of the foot, scalp or trunk.
• The lesions themselves are harmless.

Histology

In an autopsy study (14 biopsies), dermal pigment deposits of haemosiderin and melanin were found in almost all cases, often with increased epidermal melanin; marked vessel wall thickening was seen in only 4 of 14 specimens.

Diagnosis

• Clinical, based on the typical appearance; biopsy is rarely needed.
• Shin spots without known diabetes warrant testing for diabetes mellitus; in known diabetes, dermopathy is regarded as a pointer to microangiopathic complications.

Differential diagnoses

• Arterial (ischaemic) ulcer
• Necrobiosis lipoidica
• Steroid-induced skin atrophy
• Livedo reticularis
• Limited systemic sclerosis (CREST syndrome)
• Erythema ab igne

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References (selection)

1. DermNet: Skin problems associated with diabetes mellitus (Diabetic dermopathy)
2. PubMed: Diabetic dermopathy: A subtle sign with grave implications (PMID 18155320)
3. PubMed: Defining diabetic dermopathy (PMID 21762390)

Cross-references