Aetiology

Several reports have shown that smoking may predispose to the development of DLE, and exposure to ultraviolet radiation may precipitate or aggravate DLE lesions.[7][8] Non-specific injury to the skin may also precipitate the development of DLE activity within areas of trauma (known as the Koebner phenomenon). The inflammatory process characteristic of DLE is thought to be driven by autoimmune mechanisms. Associations with some major histocompatibility complex antigens have been reported, but the other genetic factors that increase the risk of DLE are not known.[9]

Pathophysiology

The precise pathophysiology of DLE and other forms of cutaneous lupus erythematosus (CLE) is not yet fully understood. Interest has been concentrated on the region of the dermal-epidermal junction as the principal site of injury, because of the detection of IgG and C3 along the epidermal basement membrane, suggesting an immune-mediated process.[10] The inflammatory cells in DLE are mostly T cells in the dermis. Chronic scarring DLE lesions have a denser inflammatory cell infiltrate, which extends into the deeper reticular dermis and/or subcutis, in contrast with acute CLE and subacute CLE lesions, which contain less dense inflammatory infiltrates confined to the upper dermis. It has been suggested that keratinocyte apoptosis may be the key event in the initiation of CLE lesions.[11] The nucleated layer of the epidermis is generally not thickened and may be atrophic. There is prominent hyperkeratosis and follicular plugging.

Classification

Cutaneous manifestations of lupus erythematosus

No formal classification exists for DLE. However, it is important to understand the various cutaneous manifestations of lupus erythematosus and how DLE fits in with these.

  • Acute cutaneous lupus erythematosus (ACLE): characterised by a typical butterfly pattern malar rash involving the central portion of the face and/or a more generalised maculopapular eruption. ACLE is strongly associated with SLE.

  • Subacute cutaneous lupus erythematosus (SCLE): characterised by a non-pruritic, non-scarring rash. SCLE may be drug induced or can occur in patients with SLE, Sjogren syndrome, and complement C2 deficiency.

  • Chronic cutaneous lupus erythematosus (CCLE): lesions are confined to the skin and oral mucosa; DLE is the most common form.

Subsets of DLE

Localised: only head and neck affected.

Disseminated: other areas affected, regardless of whether head and neck involved.

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