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A healthy woman in her mid-50s developed an extremely itchy, rapidly spreading rash on her arms and legs, which had started about 3 months previously, reported Yueping Zeng, MD, and Yanan Wang, MD, of the Peking Union Medical College Hospital in Beijing, in .

Her medical and family histories were unremarkable and she was not taking any medications. She had been previously diagnosed with eczema, for which she had used topical steroid ointments and oral compound glycyrrhizin tablets; however, these treatments had no noticeable effect on her rash, she explained.

Physical examination revealed red, ring-shaped papules measuring up to 5 mm wide, scattered on her arms and legs. A few brown flat papules scattered on her face were also noted. but these were not itchy or causing any symptoms. Her palms, soles, and oral mucosa were free of the lesions.

The clinicians ordered laboratory tests, including routine blood, liver, and kidney function, antistreptolysin O, C-reactive protein, antinuclear antibody, and rheumatoid factor tests; findings were all normal. The group obtained a biopsy specimen from an annular lesion and sent it to histopathology for analysis.

Findings included the following:

• Mild hyperkeratosis accompanied by parakeratosis
• Atrophy of the epidermis
• Well-developed cornoid lamellae with a decreased granular layer
• Individual cell dyskeratosis
• Vacuolar degeneration of the basal cell layer

Zeng and Wang also noted the presence of "a slight infiltrate of lymphocytes, histiocytes, and eosinophils in the upper dermis." They established a diagnosis of eruptive pruritic papular porokeratosis (EPPP). "Six months after the patient's first visit, the papules began to subside spontaneously without any medication, leaving sporadic brown annular keratotic lesions," they wrote.

The clinicians also discussed various differential diagnoses of EPPP, including annular lichen planus (ALP), perforating granuloma annulare (PGA), and atypical pityriasis rosea (APR).

ALP is a rare clinical variant of lichen planus, with annular lesions ranging from 0.5 to 2.5 cm in size. Lesions are marked by central clearing and annular edges that are slightly raised and usually purple to white in color. The center area is generally hyperpigmented or skin colored. Generalized eruptions of ALP are rarely reported, and few people with ALP experience pruritis. Lesions tend to develop on the axilla, penis, extremities, groin, and other areas.

Microscopic examination reveals "hyperkeratosis without parakeratosis, wedge-shaped hypergranulosis, and a bandlike lymphocytic infiltrate at the dermal-epidermal junction, whereas EPPP is associated with cornoid lamella with a decreased granular layer," Zeng and Wang wrote.

As for PGA, children are more likely to be affected. PGA "may present as an umbilicated papule with a central crust or hyperkeratotic core on the extremities or trunk with lesions that become pustular or ulcerate," they explained. Eruptions are typically not associated with symptoms, although some people have reported itching and pain.

On histological examination, PGA is notable for "mucinous collagen degeneration surrounded by palisading granulomas with transepithelial elimination of altered collagen," they noted.

When diagnosing EPPP, APR is another important condition to exclude. APR generally causes extreme pruritis, accompanied in some cases by pain and a burning sensation. APR-related lesions tend to be papular, vesicular, and purpuric, and follow a similar course to the classic form of pityriasis rosea, Zeng and Wang said.

"A herald patch is an important marker, which is seen in most of the atypical cases, and atypia is rare in herald patches," they wrote. APR rarely affects the face, scalp, hands, and feet, and involvement of the fingers, scalp, eyelids, and penis is exceptional. Histopathology findings include "focal parakeratosis in the epidermis, spongiosis, extravasation of red blood cells, and a perivascular lymphocytic infiltrate," they explained.

Discussion

Zeng and Wang noted that EPPP -- also known as eruptive disseminated porokeratosis (EDP) -- is a rare variant of porokeratosis. The condition presents with "acute exacerbation of annular papules surrounded by a distinctive hyperkeratotic ridgelike border accompanied by severe pruritus," they wrote.

In 2014, Shoimer et al. proposed according to four subtypes: paraneoplastic, immunosuppressed, inflammatory, and other type. In the current patient's case, the asymptomatic brown papules suggested disseminated superficial actinic porokeratosis, the authors noted, except for the distribution of lesions on flexor surfaces of the extremities not exposed to the sun.

They said that the classification proposed by Shoimer and colleagues suggests that the lesions on the extremities would be categorized as an inflammatory subtype of EDP, typically characterized histologically by evidence of a cornoid lamella and a dermal inflammatory infiltrate. About one-quarter to one-half of cases of EPPP "have additional eosinophilic infiltration in the vicinity of blood vessels in the upper dermis," they wrote.

In the absence of guideline-recommended treatments for EPPP, patients are often managed with topical corticosteroids and antihistamines, although response tends to be poor. The benefits of other treatments such as topical fluorouracil, etretinate, assisted freezing, and laser therapy are also unsatisfactory, the authors added. "A topical vitamin D3 analogue, maxacalcitol, may be effective against pruritic papules," they suggested.

Clinicians should screen EPPP patients for malignant neoplasms, Zeng and Wang advised. Almost one-third of patients had a ; "therefore, screening for tumors is important, if clinically indicated," they wrote. In addition, 2% of cases have been linked with viral infections.

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