SAN FRANCISCO – Three rules can guide inpatient dermatology for the most effective practice, according to Dr. Lindy P. Fox, director of the dermatology consultation service at the University of California, San Francisco.
First, more than one infection or etiology may account for the clinical picture, especially in immunocompromised patients. If there’s more than one morphology present, work up each one separately, she said.
Second, most cases require some degree of clinicopathologic correlation.
Third, for inpatient dermatology it helps to think of "zebras," because that’s how you’ll make the rare diagnosis, she said at the annual meeting of the Pacific Dermatologic Association.
Dr. Lindy P. Fox
She provided tips on some of the more common morphologies encountered in hospital dermatology:
• Morbilliform. Most commonly, morbilliform brings to mind a drug eruption, viral exanthema, graft vs. host disease (GVHD), and other entities that can present in this pattern. Rarely in immunocompromised patients, disseminated histoplasmosis, cryptococcosis, or coccidiomycosis can mimic a drug eruption, so it’s important in those situations to biopsy what you think might be a drug eruption.
Acute graft vs. host disease on average occurs 25 days after a transplant, but hyperacute GVHD occurs 14 days post transplant, so think of this before your oncologist tells you the patient’s graft hasn’t taken, she said. Two features of GVHD morbilliform eruption distinguish it from other differential diagnoses: a perifollicular accentuation, and an acral distribution around the ears, hand, and periungual areas. A patient’s nausea, vomiting, diarrhea, and hyperbilirubinemia support the diagnosis.
• Papules/papulonodules. The differential diagnosis is long – fungal diseases, septic emboli, Sweet’s syndrome, leukemia or lymphoma cutis, Kaposi sarcoma, cutaneous metastasis, and sarcoidosis, among others. But if you see purple plumb-colored papules, the list shrinks to lymphoma, Kaposi sarcoma, bacillary angiomatosis, melanoma, or cutaneous metastasis.
• Cellulitic plaques. These bring to mind cellulitis or its mimic, stasis dermatitis, as well as some deep fungal infections, carcinoma erysipeloides, neutrophilic diseases, and acute inflammatory edema of the ICU. Keep in mind that cryptococcal cellulitis is the most common presentation of Cryptococcus in an organ transplant recipient. Unlike bacterial cellulitis, it tends to be bilateral. It is almost never purely a cutaneous disease. "If you ever see Cryptococcus on the skin, you are obligated to look for the systemic source of infection," she said.
• Palpable purpura. This typically points to small or mixed-vessel vasculitis. But you can also have secondary hemorrhage into a papular process; it can be due to leukemia, lymphoma cutis, or Sweet’s syndrome; or it can be a cutaneous reaction to cytarabine. What Dr. Fox said she commonly sees are purpuric papules on the lower extremities. If looked at closely, there’s a morbilliform eruption that can spread to the trunk in a few days. Biopsy typically demonstrates spongiosis, which is a "very reassuring" sign that this is a benign and self-limiting reaction to cytarabine. The reaction may or may not recur if the patient takes the drug again. "Steroids do help, and patients do very well," she said.
• Retiform purpura. Another very long differential diagnosis can be organized by thinking about potential causes as vascular (in the vessel wall) or intravascular (in the lumen of the wall). Lumen involvement is a sign of embolization or thrombosis. "If you see concomitant thrombosis and vasculitis truly on the same day early on in lesion development, that differential diagnosis shrinks considerably. There are very few things that can do that: cryoglobulinemia, septic vasculitis, and exposure to levamisole," Dr. Fox said.
• Sclerodermoid. The long differential diagnosis includes carcinoma en cuirasse, radiation dermatitis, GVHD, scleroderma, paraffinoma, lipodermatosclerosis, scleredema, and scleromyxedema, among others. Dr. Fox said she saw an unusual presentation in a woman with "antibiotic refractory cellulitis" who had developed a migrating paraffinoma after mineral oil injections to her calves for cosmetic purposes.
• Necrotic papules/plaques. One of the many potential causes – calciphylaxis – can be thought of as analogous to a myocardial infarction that occurs in the skin, she said. Patients more often than not have a long history of vascular stenosis and medial arterial calcification. An acute thrombotic event occurs, and the patient presents with calciphylaxis with tissue ischemia, pain, and stellate purpuric plaques. "This implies that we need to think about our therapeutics differently," she said. Address the calcium, phosphorous, and parathyroid hormone, as usual, but also consider treating the thrombus with tissue plasminogen activator. Don’t use warfarin; many cases of calciphylaxis are triggered by warfarin, and the drug promotes calcification, Dr. Fox said at the annual meeting of the Pacific Dermatologic Association.