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Why has this 70-year-old man developed an itchy, widespread erythrodermic rash covering most of his body? When he presented to the dermatology clinic, he told clinicians the patchy rash had started on his scalp and face about 2 months before, and then gradually spread to the rest of his body.

As detailed by Ruth Ann Vleugels, MD, of Brigham and Women's Hospital and Harvard Medical School in Boston, and co-authors in , the patient had no fatigue, fever, night sweats, weight loss, shortness of breath, chest pain, nausea, vomiting, or diarrhea. He had not started on any newly prescribed, over-the-counter, or herbal medications before the rash came on, and his medical history did not include any skin disorders or recent viral or bacterial infections.

When he presented to the dermatology clinic, his temperature was 37.1° C (98.8° F), his blood pressure was 128/86 mm Hg, his heart rate was 110/min, and his respiratory rate was 30/min.

On physical examination, clinicians observed "confluent salmon-colored plaques composed of folliculocentric scaly papules across his body." On his trunk, these were mixed with areas of unaffected skin.

The volar aspect of the patient's hands and feet were affected by waxy, peeling scaling, and his nails were thickened and separated from the nail bed. His lower eyelid had turned outward, so he was unable to completely close his eyes.

Clinicians referred the patient to the emergency department for blood tests, which showed normal levels for both complete blood cell count and lactate dehydrogenase level. The patient was admitted to hospital, where he received intravenous fluids. The medical team applied topical triamcinolone ointment (0.1%) daily to the patient's trunk, arms, and legs, which were wrapped with warm, damp gauze and covered with dry, cotton pajamas.

Clinicians did not order any tests for myositis-specific autoantibodies, anti-dsDNA, or HLA-B27, since the dermatologic findings did not suggest that he had dermatomyositis, systemic lupus erythematosus, or reactive arthritis, respectively.

Finally, Vleugels and colleagues explained, the team decided that the patient's generalized salmon-colored plaques interspersed with areas of clear skin, known as "islands of sparing," along with waxy thickened skin on the underside of his hands and feet pointed to a diagnosis of the rare condition of erythrodermic pityriasis rubra pilaris (PRP).

The medical team ordered a skin biopsy with T-cell clonality studies to confirm the presumed diagnosis. Examination of the tissue sample from the patient's upper back, the case authors said, "revealed acanthosis with broad rete ridges, confluent hypergranulosis, and alternating orthokeratosis and parakeratosis," which supported the diagnosis of PRP.

Flow cytometry and T-cell clonality studies did not reveal any findings characteristic of Sezary syndrome, and an HIV test proved negative, Vleugels and co-authors said. They started the patient on topical triamcinolone ointment (0.1%), and he also received treatment with acitretin (50 mg daily), methotrexate (25 mg weekly), and infliximab (Remicade; 10 mg/kg every 4 weeks).

A follow-up examination 6 months later showed that the patient's erythroderma had resolved. He received oculoplastic surgery to repair his drooping lower eyelid. Three years after his initial presentation, the patient's skin had returned to normal, and he continued to receive treatment with infliximab (5 mg/kg every 6 weeks) and methotrexate (12.5 mg weekly).

Discussion

The case authors explained that erythroderma, or exfoliative dermatitis, involves widespread reddening and scaling of the skin, affecting more than 90% of the body surface area. It is considered a dermatologic because it can result in excessive loss of fluid and heat, thus putting the patient at risk of hypothermia and rigors, inadequate hydration, low blood pressure, and high-output cardiac failure. And because it damages the skin barrier, erythroderma is linked with an increased risk of cellulitis.

Erythroderma typically occurs in patients with psoriasis or eczema, but may also develop in patients with an infection such as HIV, or scabies, in those with a malignancy such as cutaneous T-cell lymphoma (CTCL), and those with an inherited skin disease. In addition, numerous medications, including antibiotics and anticonvulsants, have been noted to cause erythroderma in some patients.

is a rare, inflammatory disorder that often results in exfoliative dermatitis, especially in adults. It can affect men and women of all ages, although most cases in adults occur from the ages of 50 to 60, and in children, it typically occurs from ages 1 to 10 years.

There are six clinical subtypes of PRP, Vleugels and co-authors noted: type I (classical adult), type II (atypical adult), type III (classical juvenile), type IV (circumscribed juvenile), type V (atypical juvenile), type VI (HIV-related).

Type I is by far the most common, accounting for about 55% of all cases, the authors explained. It is characterized by waxy palmoplantar keratoderma and salmon-colored plaques, which are clearly defined among areas of unaffected skin.

The plaques usually begin to emerge on the skin above the waist, and spread downward. Other common manifestations include hyperkeratotic changes to the nails, non-scarring hair loss, and eyelid changes associated with ectropion.

In the U.S., fewer than 5,000 people have currently been diagnosed with PRP, according to the NIH's . The physiological process that gives rise to PRP is not known, Vleugels and co-authors noted, adding that in some cases, bacterial or viral infections have been thought to trigger the condition.

"Some patients with PRP type V have an autosomal dominantly-acquired or sporadic genetic variant of caspase recruitment domain family, member 14 (CARD14), which is an activator of a signaling pathway involved in inflammation," the case authors wrote.

They listed the following conditions to consider in differential of erythrodermic PRP: psoriasis, atopic dermatitis, CTCL, generalized hypersensitivity reactions, immunobullous diseases, acquired ichthyosis, and erythrokeratoderma variabilis.

The case authors explained that PRP is diagnosed based on clinical observations and histopathological findings of a skin biopsy, and in cases involving erythroderma and ectropion and/or palmoplantar keratoderma, T-cell clonality analyses should be performed to detect possible Sezary syndrome -- a distinctive form of erythrodermic CTCL with leukemic involvement of malignant T cells.

The prognosis for patients with PRP is variable depending on the subtype, Vleugels and co-authors said. Due to the paucity of research into treatment, however, there are no evidence-based treatment guidelines. Commonly used therapies include topical corticosteroids, methotrexate, systemic retinoids, phototherapy, and cyclosporine. In addition, the team said, biologic therapies including tumor necrosis factor inhibitors and anti–interleukin (IL)-17 or anti-IL-12/ have been found to improve or resolve PRP, according to existing from case reports and small case series.

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