Dermatomyositis is a chronic connective tissue disease that can be associated with an underlying internal malignancy. This connective tissue disease shares similarities with polymyositis, but the latter has no cutaneous findings. Up to one third of patients with dermatomyositis have an underlying malignancy. The myositis is often prominent and manifests as tenderness and weakness of the proximal muscle groups. The pelvic and shoulder girdle muscles are the ones most commonly affected. Dermatomyositis sine myositis is a well-recognized variant that has only the cutaneous findings; evidence of muscle involvement is absent.
Clinical Findings: Dermatomyositis has a bimodal age of onset, with the most common form occurring in the female adult population, usually between the ages of 45 and 60 years, and a smaller peak in childhood at about 10 to 15 years of age. African Americans are affected three to four times more often than Caucasians. Dermatomyositis has an insidious onset, with the development of proximal muscle weakness in association with various dermatological findings. Skin findings start slowly and are nonspecific at first. Usually, there is some mild erythema on the hands and sun-exposed regions of the head and neck. Over time, the more typical cutaneous findings become evident. Pruritus is a common complaint, and patients not infrequently complain of severe scalp pruritus well before any signs or symptoms of dermatomyositis appear.
The heliotrope rash of dermatomyositis is one of the most easily recognized and specific findings. It is manifested by periorbital edema and a light purple discoloration of the periorbital skin. The skin is tender to the touch. Hyperemia of the nail beds and dilated capillary loops are noticeable and are similar to those seen in progressive systemic sclerosis or lupus erythematous. The dilated capillary loops are best appreciated with the use of a handheld dermatoscope that serves to magnify the region of interest.
Purplish to red, scaly papules develop on the dorsum of the hands overlying the joints of the phalanges. These are not Heberden’s nodes, which are a manifestation of osteoarthritis seen as dermal swellings overlying the distal interphalangeal joints. The papules seen in dermatomyositis have been termed Gottron’s papules. Gottron’s papules may be seen overlying any joint on the hands, as well as other joints such as the elbows and knees. The skin findings on the dorsal hands have led to the term “mechanic’s hands.” This refers to the ragged appearance of the hands in dermatomyositis; they resemble the hands of a mechanic that have suffered chronic trauma, abrasions, and erosions secondary to the occupation.
The “shawl sign” is a cutaneous finding seen on the upper back and chest. The shawl sign is so named because the location is in the same area that would be covered by a shawl garment. The skin has poikilodermatous macules and patches. There is a varying amount of skin atrophy with telangiectases, mottled hyperpigmentation and h popigmentation, and erythema of the involved region.
Patients with dermatomyositis also complain of photosensitivity and notice a flare of their skin disease with ultraviolet light exposure. Children with dermatomyositis are much more prone to develop calcinosis cutis than their adult counterparts, and approximately 50% of all children with dermatomyositis will develop this feature. Calcinosis cutis manifests as tender dermal nodules or as calcifications along the muscle fascia.
Leukocytoclastic vasculitis also is seen much more frequently in juvenile dermatomyositis than in the adult form.
Dermatomyositis is a multisystem disorder. Diagnostic criteria have been established by the American College of Rheumatology. They are based on the presence of clinical, laboratory, and histological findings. Not all patients have all aspects of the disease, and the diagnosis is based on the number of the criteria fulfilled.
Inflammation of the proximal muscle groups has been well described. Patients often complain of difficulty in standing from a sitting position or in raising their hands above their heads. Patients have elevated serum concentrations of creatinine kinase, aldolase, and lactate dehydrogenase. This is indicative of muscle inflammation and breakdown. An electromyogram (EMG) can be used to evaluate the weakness and to differentiate a nerve origin from a muscle origin. A muscle biopsy, most commonly of the deltoid muscle, shows active inflammation on histological examination.
This disease can rarely manifest with severe, diffuse interstitial pulmonary fibrosis. Patients with pulmonary fibrosis most often test positive for the anti-Jo1 antibody. Anti-Jo1 antibodies have been found to be targeted against the histidyl transfer RNA synthetase protein. Overall, it is an uncommon finding except in dermatomyositis patients with pulmonary disease. More than 75% of patients with dermatomyositis test positive for antinuclear antibodies (ANA). Those with malignancy-associated dermatomyositis typically do not develop pulmonary fibrosis, and those with pulmonary fibrosis do not develop a malignancy.
The malignancy most commonly associated with dermatomyositis is ovarian cancer. Many other malignancies have been seen in association with dermatomyositis, including breast, lung, lymphoma, and gastric cancers. Malignancy is seen before the onset of the rash in about one third of the cases, concurrently with the rash in one third, and within 2 years after diagnosis of the dermatomyositis in one third. After the diagnosis of dermatomyositis, it is imperative to search for an underlying malignancy and to perform age-appropriate cancer screening. Childhood dermatomyositis is rarely associated with an underlying malignancy.
Pathogenesis: The exact etiology of dermatomyositis is unknown. It has been theorized to occur secondary to abnormalities in the humoral immune system. The precise mechanism is under intense research.
Histology: Histological examination of a skin biopsy specimen shows an interface lymphocytic dermatitis. Hydropic change is seen scattered along the basilar cell layer. The epidermis has varying degrees of atrophy. A superficial and deep periadnexal lymphocytic infiltrate is common. The presence of dermal mucin in abundance is another histological clue to the diagnosis. A muscle biopsy often shows atrophy of the involved muscle with a dense lymphocytic infiltrate.
Treatment: There is no known cure for dermatomyositis, although some cases spontaneously remit. Cases associated with an underlying malignancy have been shown to go into full remission with cure of the underlying cancer. Relapse of dermatomyositis in these patients should prompt the clinician to search for a recurrence of their malignancy. Initial treatment is usually with prednisone, which acts as a nonspecific immunosuppressant. The addition of a steroid-sparing agent is almost always needed to avoid the long-term side effects of prednisone. Some patients require a smaller dose of prednisone along with a steroid-sparing agent to keep the disease at bay. Many steroid-sparing agents have been used, including hydroxychloroquine, quinacrine, cyclosporine, intravenous immunoglobulin (IVIG), azathioprine, and methotrexate, all with variable success. Combination therapy is the norm.
The use of sun protection and sunscreen cannot be overemphasized. Topical corticosteroids help relieve the itching and decrease some of the redness. The treatment of juvenile dermatomyositis is similar. It is believed to have a better prognosis, because few cases are associated with an underlying cancer. It is thought that early treatment of juvenile dermatomyositis decreases the risk of developing evere calcinosis cutis during the course of the disease.