Dermatomyositis
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.
