Discoid lupus erythematosus
Cutaneous lupus erythematosus (CLE) can be divided into 3 main subtypes: acute, subacute, and chronic, all of which demonstrate photosensitivity. Acute cutaneous lupus erythematosus (ACLE) most commonly presents as symmetric erythema overlying the malar cheeks and nasal bridge with sparing of the nasolabial folds (butterfly rash). However, it can also present as a diffuse morbilliform eruption with erythema and edema of the hands, with prominent sparing of the joints. Subacute cutaneous lupus erythematosus (SCLE) characteristically presents as annular or psoriasiform plaques in a photodistribution. Chronic cutaneous lupus erythematosus (CCLE) can be further divided into 3 main types: discoid lupus erythematosus (DLE), tumid lupus, and lupus panniculitis. Tumid lupus typically presents with juicy papules and plaques that heal without scarring, whereas lupus panniculitis involves the subcutaneous tissue, leading to painful subcutaneous nodules that heal with depression and atrophy.
DLE classically presents with erythematous-to-violaceous, scaly plaques with prominent follicular plugging that often results in scarring and atrophy (see the images below). DLE may occur in the absence of systemic disease, or it may occur in association with systemic lupus erythematosus (SLE).
The risk of progression to SLE in patients with DLE was demonstrated to be higher than previously reported (16.7% progression within 3 years of diagnosis, as compared with previous data indicating that < 5-10% of patients with DLE progress to SLE). [1, 2] Overall, patients with DLE rarely fulfill 4 or more of the 11 American College of Rheumatology (ACR) criteria used to classify SLE.  Serologic abnormalities are uncommon.
Therapy with sunscreens, topical corticosteroids, and antimalarial agents is often effective. (See Clinical and Treatment.) However, immunosuppressive and/or immunomodulatory agents may be required for recalcitrant disease.
Lupus erythematosus is a polygenic autoimmune disease linked to various HLA subtypes, immune signaling, and environmental factors, which ultimately leads to autoantibody production and T-cell dysfunction. However, the exact etiology of discoid lupus erythematosus (DLE) is not well understood. DLE likely occurs in genetically predisposed individuals, but the exact genetic connection has not been determined. It has been suggested that a heat-shock protein is induced in the keratinocyte following ultraviolet (UV) light exposure or stress, and this protein may act as a target for gamma (delta) T-cell–mediated epidermal cell cytotoxicity. Additionally, toll-like receptors may be involved in the pathogenesis.
Worldwide, the prevalence of systemic lupus erythematosus (SLE) ranges from 17-48 cases per 100,000 population. The highest prevalence of SLE occurs in persons aged 40-60 years, with SLE onset most often occurring in patients in their 20s and 30s. SLE is approximately 10 times more common in women than in men. In a 2009 study from Olmstead County, Minnesota, Durosaro et al demonstrated that the incidence of cutaneous lupus erythematosus (CLE) is comparable to that of SLE. 
Discoid lupus erythematosus (DLE) is responsible for 50-85% of cases of CLE and occurs 2-3 times more frequently in women than in men. DLE is slightly more common in African Americans than in whites or Asians. Although DLE may occur at any age, it most often develops in persons aged 20-40 years.
Although the prognosis of patients with discoid lupus erythematosus (DLE) is favorable regarding mortality, morbidity can be considerable. Patients may experience pain or burning of their lesions, and many experience disfigurement from the scars or atrophy that can develop. Scarring alopecia is particularly disturbing for patients. Prompt treatment of early lesions may help prevent or lessen the severity of scarring and atrophy.