Derm Dx: Red-Brown Papules on the Extremities

Pityriasis Lichenoides Chronica and Pityriasis Lichenoides et Varioliformis AcutaPityriasis lichenoides (PL) is a benign, self-limited inflammatory cutaneous condition. Historically, defining PL has been quite challenging as it was at one time confused as a form of parapsoriasis.1 Over time, however,...

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Pityriasis Lichenoides Chronica and Pityriasis Lichenoides et Varioliformis Acuta

Pityriasis lichenoides (PL) is a benign, self-limited inflammatory cutaneous condition. Historically, defining PL has been quite challenging as it was at one time confused as a form of parapsoriasis.¹ Over time, however, the disorder has been better characterized and is now described along a spectrum, ranging from the more chronic form, pityriasis lichenoides chronica (PLC), to the more acute-phase disorder, pityriasis lichenoides et varioliformis acuta (PLEVA), also known as Mucha-Habermann disease.² The terms acute and chronic used in this context do not refer to the onset or duration of the disease itself but to the characteristics of the lesions present on the affected individual.³ PLEVA and PLC are viewed as 2 diseases on a spectrum rather than 2 separate entities.

Both PLC and PLEVA are rare disorders; therefore, the exact prevalence, incidence, and risk factors have not been well documented. Although the disorders appear to occur more frequently in children and young adults, they have the potential to occur at any age. Studies have shown a slight male predominance among children with PL, but this gender predominance has not been observed in the general population of individuals with PL.²

The pathogenesis of PL has yet to be clearly described. Some research has suggested that there may be associations with an aberrant immune response to bacterial, viral, or protozoal infections that lead to the development of the disease.⁴ More recent studies pose the hypothesis that PL is a lymphoproliferative disorder, existing at the benign end of the spectrum with lymphocytic malignancy.^5,6

In both PLC and PLEVA, patients tend to experience waves of eruptions of papules, with multiple relapsing and remitting cycles before spontaneous resolution occurs. The entire duration of symptoms can range from weeks to years, with the median duration of disease in PLEVA and PLC lasting approximately 18 and 20 months, respectively.⁷

The development of PLC typically occurs gradually and results in erythematous papules that have a reddish-brown hue and a micaceous scale in the center. These eruptions occur most commonly on the trunk, buttocks, and proximal portions of the extremities and, unlike PLEVA, spontaneously flatten and regress over a period of weeks. Aside from the lesions, patients with PLC are usually otherwise asymptomatic. After resolution of the papules, patients are commonly left behind with hypopigmented macules in the areas where the lesions previously existed.⁸ In contrast to PLC, PLEVA begins as an acute eruption of erythematous papules and macules measuring approximately 2 to 3 mm in diameter that quickly develop into papules with progressively thickening scales. These lesions, like in PLC, often occur on the trunk and proximal areas of the extremities; however, unlike in PLC, they can also display a generalized eruption pattern.² Associated burning and pruritus occur more commonly in patients with PLEVA, whereas those with PLC generally lack symptoms outside of the lesions themselves.

Disorders that may be considered in the differential diagnosis for PLEVA include varicella, disseminated herpes simplex virus (HSV), arthropod bites, Gianotti-Crosti syndrome, and Langerhans cell histiocytosis. Varicella and disseminated HSV may be differentiated from PLEVA using polymerase chain reaction or direct fluorescence antibody testing. Arthropod bites rarely have necrotic findings and a thorough patient history is useful for diagnosis. Gianotti-Crosti syndrome and Langerhans cell histiocytosis can both be differentiated using information obtained from a skin biopsy.⁹

Disorders that may be considered in the differential diagnosis for PLC include lymphomatoid papulosis (LyP), pityriasis rosea, guttate psoriasis, lichen planus, secondary syphilis, and hypopigmented mycosis fungoides. LyP, unlike PLC, heals with scarring. Pityriasis rosea has a shorter resolution time frame. Guttate psoriasis is usually preceded by a streptococcal infection. Lichen planus is often accompanied by pruritus and may also be present on the mouth, genitals, and nails. Secondary syphilis often involves the palms and soles, and serologic studies can confirm the diagnosis. Hypopigmented mycosis fungoides can be successfully differentiated via skin biopsy.¹⁰

The diagnosis of PLC and PLEVA can be made clinically, as PLEVA is typically characterized by the eruption of acute, crusting, hemorrhagic papules, whereas PLC is characterized by red-brown papules with a micaceous scale covering.² However, if the diagnosis is uncertain, punch biopsy followed by histologic examination of the tissue can confirm the diagnosis.⁷ Histologic findings characteristic of PLC include focal parakeratosis, spongiosis, band-like (lichenoid) lymphohistiocytic infiltrate in the superficial dermis, and superficial vessel dilation with no invasion of the vessel wall by inflammatory cells.² The histologic characteristics seen in PLEVA include a more severe, diffuse parakeratosis, spongiosis, focal necrotic keratinocytes, vacuolar alteration of the basal layer, dense wedge-shaped lymphohistiocytic infiltrates into the deep reticular dermis, and engorgement of blood vessels in the papillary dermis with extravasation of erythrocytes and lymphocytes.²  Immunohistochemical stains can also be used for the diagnosis of PLEVA, which would show a predominance of CD8+ T lymphocytes and an absence of CD30+ cells in the inflammatory infiltrate. This staining can be particularly useful for differentiating PLEVA from the clinically similar LyP. 

Both PLC and PLEVA are benign, self-limiting conditions that can be managed with observation and close follow-up. Pharmacologic treatment is not required; however, patients concerned with the cosmetic disfiguration associated with the lesions frequently desire treatment. In these cases, the first-line regimen includes topical corticosteroids in combination with oral antibiotics. Topical corticosteroids, such as triamcinolone (0.1% cream), have been shown to hasten lesion clearance in some patients.¹¹ Oral antibiotics, most commonly tetracycline in adults and erythromycin in children, are often prescribed to be used in conjunction with the topical steroids.^7,12 Second-line therapies include narrowband ultraviolet B (UVB) phototherapy, broadband UVB, psoralen plus UVA (PUVA), and methotrexate.¹³

In this case, the clinical picture and skin biopsy were both consistent with PL. Treatment was initiated with topical corticosteroids and oral antibiotics (erythromycin). The patient responded well to therapy, with near complete resolution of his lesions.

Junru Yan, BA, is a medical student; Joan Fernandez, BS, is a medical student; and Christopher Rizk, MD, is a dermatology resident at Baylor College of Medicine in Houston, Texas.

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