Answer: B

A biopsy from a lesion demonstrated an interface dermatitis with mild vacuolar changes and a mild to moderate perivascular, lymphocytic infiltrate confirming the suspected diagnosis of pityriasis lichenoides (PL), most consistent with pityriasis lichenoides chronica (PLC).  

The term PL describes a spectrum of skin disorders with 3 variants: pityriasis lichenoides et varioliformis acuta (PLEVA), PLC, and febrile ulceronecrotic Mucha-Habermann disease (FUMHD). Although each variant has a somewhat different presentation and prognosis, considerable overlap exists in their clinical, histopathologic, and etiologic aspects suggesting that they be considered a continuum of the same disease process.1

Of these, PLEVA, also known as Mucha-Habermann disease, is a more acute-to-subacute disease process. Lesions, which are often exuberant, consist of vesicles, pustules, crusted papules, and shallow ulcers. Pityriasis lichenoides et varioliformis acuta is typically self-limited with lesions healing in weeks to months, sometimes with scarring.

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Febrile ulceronecrotic Mucha-Habermann disease is a rare variant. It develops abruptly either de novo or in association with preexisting PLEVA or PLC. It is the most fulminant variant with fever, constitutional symptoms, multiorgan injury, and ulceronecrotic lesions. It carries up to a 25% mortality rate.1

Pityriasis lichenoides chronica, as its name suggests, is a chronic form of PL. It is also the most common and subtle of the 3 variants. The onset of PLC is usually gradual, presenting with small, red-brown macules and papules with a fine central scale. However, especially in darkly pigmented children, the condition may present with hypopigmented macules.2 Areas most affected include the trunk, flexural regions, and proximal extremities. Pityriasis lichenoides chronica is typically a self-limited process, following an indolent course. Outbreaks generally wax and wane over many months although rare cases may persist for several years. Lesions heal over time without scarring. Curiously, the areas of involvement may predict prognosis: cases with a generalized eruption may demonstrate a shorter course, whereas those with an acral distribution may persist for years.2

Although the true incidence of PL is unknown, it is estimated to occur in 1 in every 2000 people, with approximately 20% of cases occurring in children.3 The peak incidence in adults is the third decade of life whereas the peak age in children is between 5 and 10 years, with the average age being 6.5 years.2,3 Children tend to have a more generalized eruption including involvement of the face.2

The diagnosis of PLC may be suspected from the clinical presentation, but confirmation requires a biopsy. Histology shows a superficial, CD4+ dominant, perivascular lymphocytic infiltrate with interface dermatitis, mild focal parakeratosis, few extravasated erythrocytes, and minimal necrosis.1,4 Typically, PLEVA and FUMHD will show similar findings but with more necrosis, hemorrhage, and denser lymphocytic infiltrate, though overlap is common.

Pityriasis lichenoides appear to be a T-cell-mediated process that is often associated with monoclonal lymphocytic proliferation. Although the precise etiology of PL remains elusive, 3 main theories prevail. Some believe it to be an inflammatory response to an infectious agent, others think it is a drug-related hypersensitivity reaction, and yet others consider it to be a primary lymphoproliferative disorder. Clinical and scientific data support all 3 theories.1,4

The infection-mediated theory is supported by the following: PL outbreaks occur during the fall and winter, are often accompanied by an upper respiratory system infection, are described in association with tonsillitis, and are usually self-limited.2 Historically, a variety of infections have been associated with PL including Epstein-Barr virus, cytomegalovirus, varicella-zoster virus, HIV, adenovirus, parvovirus B19, hepatitis C virus, staphylococcus, Mycoplasma pneumoniae, and Toxoplasma gondii infections. In some studies, up to 30% of PL cases follow an infection.

Various medications have also been linked with PL including some chemotherapeutic, antibiotic, and antipyretic agents, as well as a variety of vaccines such as measles-mumps-rubella, influenza, and hepatitis B.2

The presence of a monoclonal lymphocytic proliferation and numerous reports of malignant features in some forms of PL and rare cases transforming into cutaneous lymphomas support the hypothesis that PL is within the spectrum of a malignant lymphoproliferation process. However, monoclonality can be seen in benign processes and the transformation to lymphoma is rare, mostly following FUMHD.

The differential diagnosis of PLC includes its variants PLEVA and FUMHD as well as pityriasis rosea, guttate psoriasis, lichen planus, secondary syphilis, lymphomatoid papulosis, and mycosis fungoides. Clinical and histologic features will usually delineate the various diagnoses.

Treatment is warranted to prevent progression to more aggressive forms of PL, improve the cosmetic appearance, and prevent the rare transition to malignancy.  

Although a myriad of topical and systemic agents have been tried, the available evidence is limited and there remains no standard regimen.5 Therapeutic options range from conservative use of topical steroids and calcineurin inhibitors to the use of systemic antibiotics, antihistamines, and phototherapy as well as to a more aggressive approach with immunosuppressants such as methotrexate and cyclosporine.6-8 Overall response to therapy is high, ranging from 70% to 100%.6 However, more aggressive management is reserved for the more aggressive cases of PL.

Numerous reports tout the efficacy of oral tetracyclines and macrolides to treat PL.2,6  Clearance has been noted after 1 to 3 months of erythromycin therapy, although a few studies report early relapse and others report only partial improvement.2,6,9 As with any macrolide, there is a risk of QT interval prolongation so its use should be avoided in those with a risk for arrhythmias. Tetracyclines, particularly minocycline, may induce complete remission within a few months. However, few studies have investigated the use of tetracyclines for PL, and tetracycline use may be contraindicated in children younger than 8 years of age.6 The duration of antibiotic therapy should be at least 2 to 3 months to decrease the risk of relapse but treatment duration may be limited by gastrointestinal upset.2

To date, of all therapies investigated for PLC, phototherapy has been the most successful.2 All forms of phototherapy appear to have some benefit: heliotherapy (natural sunlight), PUVA, UV-A1, and narrowband UV-B (NBUVB).6 The number of phototherapy sessions needed to see an effect range from 10 to 40 depending on the modality selected.2,3,6 A taper of therapy, postresponse, may prevent disease relapse.

Treatment with NBUVB is considered safe in the pediatric population, although UV light exposure should always be minimized. As such, oral erythromycin or NBUVB phototherapy should be considered first-line therapies for PLC in pediatric cases.1,10 Our patient was placed on oral erythromycin and followed closely. Six weeks later his skin was nearly clear. Had he not responded, the next step would have been NBUVB phototherapy.

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