pediatric dermatology Pityriasis Lichenoides Devang G. Patel, MD George Kihiczak, MD Robert A. Schwartz, MD, MPH Camila K. Janniger, MD W. Clark Lambert, MD, PhD Pityriasis lichenoides (PL) is a skin disorder of un- PL from small and large plaque parapsoriasis, includ- known etiology that mainly affects children and young ing digitate dermatosis, xanthoerythrodermia perstans, adults. Pityriasis lichenoides is perhaps best considered and the rare entity, retiform parapsoriasis. a disease spectrum with acute and chronic types: pityr- iasis lichenoides et varioliformis acuta (PLEVA) and Incidence pityriasis lichenoides chronica (PLC). Pityriasis Pityriasis lichenoides most commonly occurs in chil- lichenoides et varioliformis acuta, the acute variant, is dren and young adults; however, its precise incidence characterized by the onset of papulovesicular eruptions is unknown. Both PLC and PLEVA appear to be that evolve into necrotic lesions over the trunk and about as common in males as in females, with PLC extremities, and hence the name “varioliformis,” occurring more frequently. Pityriasis lichenoides et which means “like variola” (like smallpox). Pityriasis varioliformis acuta most often occurs during the sec- lichenoides chronica, the chronic form, involves re- ond or third decade of life. However, the disease may current crops of papules that may last from several also arise in children and the elderly, and may even months to several years. Both types are further char- be evident at birth.10 There is no apparent racial or acterized by independent evolution of each lesion, so geographic predisposition.1,2 that lesions in all different states of progression are found next to each other in a random array. A third Characteristics disease, lymphomatoid papulosis (LP), is also included Pityriasis lichenoides is perhaps best considered as a in this grouping by some authors. Pityriasis lichenoides disease spectrum with three forms: PLEVA, PLC, and is regarded under the rubric of parapsoriasis, although LP. There is controversy regarding the inclusion of it is distinct from large and small plaque parapsoriasis, LP into the PL spectrum. Pityriasis lichenoides et var- the other principle entities that comprise the parapso- ioliformis acuta, also known as Mucha-Habermann riasis grouping.1-3 disease, is characterized by the acute onset of firm, pinkish papules, 2- to 10-mm in diameter, associated History with dense inflammatory infiltrates.1,11 The papules Pityriasis lichenoides was first described in 1894 by commonly involve glabrous skin over the entire body Jadassohn4 and Neisser5 in two separate reports. The surface with relative uniformity (Figures 1 to 3).12,13 chronic form was described again by Juliusberg6 in 1899 The lesions generally occur on the anterior trunk and and given the name PLC. In 1902, Brocq7 classified PL flexor surfaces and tend to be more numerous on the under the group parapsoriasis, which he proposed has proximal rather than distal parts of the extremities.14 guttate, plaque, and lichenoid variants. Mucha8 in An important diagnostic sign is that lesions at all dif- 1916, and later Habermann9 in 1925, described acute ferent stages are present at the same time in close PL as a disease entity distinct from the other parapso- proximity to each other. The face, palmoplantar sur- riases, including PLC. In 1981, Lambert and Everett1 faces, and mucous membranes are usually spared. Pru- reclassified the parapsoriasis group to clearly delineate ritus is sometimes present, but the lesions are more often asymptomatic.12-14 As PL progresses, the papules become hemor- From Dermatology, Pediatrics, and Pathology, New Jersey rhagic, vesicular, necrotic, and crusted, leaving scars Medical School, Newark, New Jersey. REPRINT REQUESTS to the Department of Dermatology, New with postinflammatory hyperpigmentation or hy- 15 Jersey Medical School, 185 South Orange Avenue, Newark, New popigmentation. The patient’s general health is usu- Jersey 07103-2714 (Dr. Janniger). ally unaffected; however, low-grade fever, generalized VOLUME 65, JANUARY 2000 17 PITYRIASIS LICHENOIDES FIGURE 1. Recurrent crops of sessile pinkish papules. lymphadenopathy, malaise, and headache are occa- glabrous skin over the whole body surface, a central sionally seen.2 A rare acute febrile ulceronecrotic type variety involving the neck, trunk, and proximal ex- of PLEVA, known as “febrile ulceronecrotic Mucha- tremities, and a peripheral form with an acral distri- Habermann disease,” has been noted to occur in chil- bution.12,13 The diffuse type usually has the shortest dren. This severe form of PLEVA is characterized by duration and the peripheral type has the longest. the acute onset of diffuse, coalescent, large, ul- Lymphomatoid papulosis, a PL variant, is charac- ceronecrotic skin lesions often associated with a high terized by the uninterrupted appearance of papu- fever. A mild eruption is usually observed before the lonecrotic, nodular, and occasionally large, plaque-like, acute fulminating course.2,3 Pityriasis lichenoides et self-healing eruptions that undergo exacerbations and varioliformis acuta usually follows an acute course remissions for an indefinite period of time. The lesions that spontaneously resolves in several weeks. How- show some histologic features resembling malignant ever, after an acute phase, PLEVA may change into lymphoma, but are clinically benign.18-23 It may be clin- PLC, which has a prolonged chronic course.14 ically difficult to distinguish LP from PLEVA. How- Pityriasis lichenoides chronica is characterized by ever, LP lesions tend to be nodules and plaques, recurrent crops of lichenoid, reddish-brown papules whereas PLEVA lesions are papular, more necrotic that are covered by a light scale and generally invo- than vesicular, less numerous, and evolve slowly. The lute within 3 to 6 weeks. This solitary micaceous scale most significant difference between the two is that on the papule can easily be scraped off to demonstrate about 10 to 20% of patients with LP eventually de- a typical shiny brown surface. Papules tend to flatten velop mycosis fungoides (MF), Hodgkin’s disease, or into a hyperpigmented, gradually fading macule. The non-Hodgkin’s lymphoma.16 Conversely, patients with disease may last from several months to several years MF may develop lesions that are clinically and histo- with frequent exacerbations and remissions.1,2,6,16,17 The logically identifiable as LP.24 differentiation between PLEVA and PLC is some- times unclear. Patients may have lesions of both the Histopathology acute and chronic form simultaneously, as well as The histology of the three entities comprising PL are transitional lesions. This suggests that PLEVA and distinct.21,24-28 In PLEVA, the epidermis shows inter- PLC may be a continuous spectrum of the same dis- cellular and intracellular edema, focal necrosis, and, ease process, rather than two distinct entities.2,12,13 Be- occasionally, neutrophils in the stratum corneum. cause of the frequent association between the two PL The dermis has pronounced perivascular and diffuse variants, Gelmetti et al.12 suggested an alternative infiltrates, consisting mainly of mononuclear cells, classification. They described three patterns based on and extravasation and diffusion of erythrocytes into anatomic distribution: a diffuse form involving the epidermis. The vascular changes consist of en- 18 CUTIS® PITYRIASIS LICHENOIDES FIGURE 2. Close-up of the papules in Figure 1. dothelial swelling and hemorrhage, with small de- liformis acuta, PLC, and LP have several immuno- posits of fibrin present within vessel walls. histologic similarities.30 All three diseases are charac- Pityriasis lichenoides chronica characteristically terized by an infiltrate of activated T cells mixed with features dermal–epidermal interface dermatitis in all macrophages in the epidermis and dermis.27-32 Both stages of the lesions. Lymphocytes and histiocytes, PLEVA and LP have been shown, in some cases, to melanophages, and extravasated erythrocytes are the undergo rearrangement of T cell receptor genes, in- cells most commonly observed. Focal mild paraker- dicating a clonal T cell lymphoproliferative process. atosis may also be seen.29 This finding supports the hypothesis that these three Both PLEVA and PLC show a distinctive pattern in entities represent a spectrum of a single disease. their dermal inflammation, which is wedge-shaped. The The presence of IgM and C3 in the dermal vessel apex of the wedge is deep and the base is at the der- walls and along the dermal–epidermal junction has mal–epidermal interface, which is covered by the epi- been demonstrated in patients with PLEVA. Sero- dermal component of the disease. Within this wedge, logic, epidemiologic, and therapeutic evidence sug- the inflammation is often focused around blood vessels. gests that PLEVA may be the result of a hypersensi- In LP, two types of atypical cells, histiocytes and tivity reaction to an infectious agent,32 although a lymphocytes, are seen, with either one or the other specific agent has not been isolated with reproducible predominating. When histiocytes predominate, the results in patients with PLEVA. The above data sug- condition is called “Willemze Type A,” and when gest that PL may be due to persistent antigen stimu- lymphocytes are prevalent, the condition is known lation and resulting immune complex deposition. as “Willemze Type B.” In Type A LP, the atypical cells are characteristically large with pleomorphic, Differential Diagnosis bizarrely-shaped