SNOWMASS, COLO. – Nondermatologists often have a dickens of a time differentiating the malar rash that’s a hallmark of systemic lupus erythematosus from butterfly midfacial rashes due to other diseases, most notably rosacea and dermatomyositis. Dr. Ruth Ann Vleugels has provided some useful tips.
The malar rash of systemic lupus erythematosus (SLE) consistently spares the nasolabial folds, for reasons unknown. So, if a red, butterfly-shaped rash on the central face involves the nasolabial area, it’s not SLE, she explained at the symposium.
In contrast, when the erythrotelangiectatic or papulopustular variants of rosacea blanket the midface with a rash that looks much like the malar rash of SLE, the nasolabial area is included, not spared.
Dr. Ruth Ann Vleugels
"Rosacea with a rash on the malar area and photosensitivity are very common in young, fair-skinned women, as is lupus. These patients with rosacea often get [antinuclear antibody (ANA)] testing. A lot of them will be positive, so already they have three ACR criteria for SLE, and they end up in your office," said Dr. Vleugels, a dermatologist who is director of the connective tissue disease clinic at Brigham and Women’s Hospital and codirector of the rheumatology-dermatology clinic at Children’s Hospital, Boston.
Alopecia and hemorrhagic crusting on the lips are common in patients with SLE, not so in rosacea. Also, patients who present with rosacea are usually in general good health, whereas those with the malar rash of SLE often feel sick and have systemic findings at presentation.
It’s helpful to ask whether the patient has noticed if the rash has other triggers in addition to sunlight. Alcohol and spicy foods are two of the most common ones in rosacea.
Midfacial erythema that includes rather than spares the nasolabial folds is also a characteristic finding in dermatomyositis. Nailfold findings provide another important cutaneous clue to the diagnosis of dermatomyositis. The changes to look for are dilated capillary loops, thrombosed capillary loops, capillary dropout, and cuticular hypertrophy.
The shawl sign – a diffuse, flat erythema on the upper back and chest – is another clue suggestive of dermatomyositis. The eruption is inflammatory early on and more atrophic later.
Mechanics’ hands, with cracked skin at the tips of the fingers, is another skin finding in dermatomyositis, Dr. Vleugels continued.
A poikiloderma known as the holster sign, so named because of its location on the lateral upper thigh, is a common finding in dermatomyositis patients. The sun-protected location is something of a mystery given that dermatomyositis is a photo-exacerbated disease.
Scalp disease is extremely common in patients with dermatomyositis, and it is strikingly pruritic.
A heliotropic skin eruption and Gottron\'s papules are considered pathognomic for dermatomyositis, but these can be tricky. The heliotrope rash is classically a prominent violaceous erythema on the eyelids; however, it’s often a subtle abnormality that waxes and wanes. And the classic violaceous Gottron’s papules found only over the knuckles are tough to detect in darker skinned patients. When Gottron’s papules are scaly they can be misdiagnosed as psoriasis. Dr. Vleugels has even seen them misdiagnosed and treated as warts.
Skin biopsy is typically of little value in differentiating lupus from dermatomyositis. The pathology report can be the same in both conditions: vacuolar interface changes at the basement membrane, with mucin in the dermis.
"If the report reads ‘lupus’ you always have to put dermatomyositis in the differential diagnosis, and the decision is a purely clinical one," Dr. Vleugels advised.
She reported having no financial conflicts.