SCLE is a diagnosis based on clinical presentation, in conjunction with results from histopathology, immunofluorescence, and serology. Notably, drug-induced SCLE may differ from idiopathic SCLE in that drug-induced SCLE are more likely to cause malar rash accompanied by bullous erythema multiforme and vasculitic manifestations. In SCLE, histology reveals a thin epidermis, with slight lymphocytic perivascular and perifollicular inflammatory infiltrate in the superficial and deep dermis. Follicular plugging, hyper-orthokeratosis, and parakeratosis are less common than with other forms of lupus erythematosus, such as discoid lupus. The epidermis in SCLE lesions displays extensive damage of all layers, with eosinophilic necrosis and vacuolization. The majority of patients have a positive immunopathologic lupus band test, meaning that complement and or immunoglobulin is present along the dermal-epidermal junction. Serology in SCLE is often positive for ANA and is more likely than SLE to be associated with positive SS-A and SS-B autoantibodies. Anti-histone antibodies are present in more than 95 % of cases of drug-induced SCLE.

The average resolution time upon discontinuing the inciting drug is approximately 7 weeks. Several studies attempted treatment before discontinuing the drug, with no resolution noted until the drug was eventually terminated. Most lesions resolve without additional treatment. However, a few reported cases in the literature have required active treatment for resolution of drug-induced SCLE to occur; the inciting drugs in these cases were terbinafine, leflunomide, anastrazole, leuprorelin, and psoralen plus ultraviolet A (PUVA) therapy. Treatment was initiated with topical steroids such as clobetasol, oral prednisone, hydroxychloroquine, topical tacrolimus, or mycophenolate mofetil. In several follow-up appointments, most patients who were originally anti–Ro or La positive did not convert to negative upon resolution. This signified that once a patient seroconverted, he or she remained positive for the antibodies associated with the disease despite treatment and resolution of symptoms.

Some pathognomonic skin findings of DM are the heliotrope rash, Gottron’s papules, mechanic’s hands (Fig. 16.3), Holster shawl, V-signs, and malar rash. The heliotrope rash (named for the purple flower) is described as an erythematous to violaceous eruption around the upper eyelids associated with swelling. The heliotrope rash is often tender to touch as it can involve the orbicularis oculi muscle. Gottron’s papules consist of erythematous to violaceous papules that erupt symmetrically along the extensor surfaces of the metacarpophalangeal and interphalangeal joints (Fig. 16.4), although the term is sometimes used to refer to similar lesions on the medial malleoli. The papules can become scaly and ulcerate. Mechanic’s hands are hands whose palms and lateral finger surfaces are thickened (hyperkeratotic). Holster sign signifies similar lesions on the hips, shawl sign is erythema of the upper back and shoulders, and V-sign is erythema of the V-area of the neck and chest. Holster sign is significant for the fact that it is outside of the typical photodistributed pattern of presentation. Poikiloderma—hyperpigmented and hypopigmented lesions that contain small telangiectasias with epidermal atrophy—may be observed along with erythema in the areas of the shawl and V-signs. The lesions are typically quite pruritic and may become thickened and palpable. Facial erythema can also be present and is similar to the characteristic malar rash of SLE; however the erythema involves the nasolabial skin folds that are typically spared in SLE and SCLE. Cuticle overgrowth and periungual changes may occur, particularly in the capillary nail beds. In addition, vascular changes can occur with areas of dilation presenting as erythematous changes elsewhere on the body.

The “myositis” element of DM consists of symmetric proximal muscle weakness with edema and myalgias. The most common locations for these findings are the deltoids and hip flexors. Classic presentations and complaints are related to patients’ subsequent inability to climb stairs, comb their hair, or lift light objects over their heads. Involvement of bulbar muscles can cause difficulty swallowing, and potential involvement of respiratory muscles can make speaking and even breathing difficult. Finally, in the terminal phases of the illness, cardiac muscle involvement produces cardiac failure.

Many drugs have been reported to induce a DM-like eruption (Fig. 16.5). The agents most frequently implicated are hydroxyurea, penacillamine, and zoledronic acid, however other medications can cause the disease as well (Table 16.2). Case reports dominate the literature and review indicates that different drugs can induce different manifestations of DM. Humoral immunity and vasculopathy caused by complement deposition are most likely responsible for the muscular changes in DM. The causes of dermatologic findings are less clear, although it has been posited that the reaction is associated with the development of autoantibodies through the unmasking of sequestered antigens when the drug is introduced to bodily tissues.