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INTRODUCTION — Pityriasis lichenoides is a term used to refer to a group of rare acquired inflammatory skin disorders that includes pityriasis lichenoides chronica (PLC), pityriasis lichenoides et varioliformis acuta (PLEVA), and the febrile ulceronecrotic Mucha-Habermann disease (FUMHD) variant of PLEVA. The use of the term pityriasis lichenoides to refer to all three disorders is representative of the theory that PLC, PLEVA, and FUMHD may represent a clinical spectrum of a single disease.
PLC is clinically characterized by the development of multiple, scaly, erythematous to brown papules on the trunk and extremities. The condition usually has a relapsing and remitting course that persists for months or years.
The clinical manifestations, diagnosis, and management of PLC will be reviewed here. PLEVA is discussed separately. (See "Pityriasis lichenoides et varioliformis acuta (PLEVA)".)
EPIDEMIOLOGY — Definitive conclusions on the epidemiology of pityriasis lichenoides chronica (PLC) are hindered by the frequent lack of distinction between the subtypes of pityriasis lichenoides in the published literature and limited data. In general, PLC is considered a rare disorder that is most likely to occur in young adults and children . However, PLC may develop at any age.
The existence of sex, ethnic, or racial predilections in PLC is uncertain . Based upon data from a few retrospective studies of children with pityriasis lichenoides, there may be a slight male predilection for pityriasis lichenoides in the pediatric population [3-7]. In one of the largest series of children with PLC (n = 46), 59 percent of the children were male .
PATHOGENESIS — The pathogenesis of pityriasis lichenoides chronica (PLC) is poorly understood. Concordant with the view that PLC and pityriasis lichenoides et varioliformis acuta (PLEVA) may be related disorders, the major pathogenic theories for PLC and PLEVA overlap. These theories include the classification of PLC and PLEVA as hypersensitivity responses to infection or as primary lymphoproliferative disorders. (See "Pityriasis lichenoides et varioliformis acuta (PLEVA)", section on 'Pathogenesis'.)
Consideration of an infectious trigger for pityriasis lichenoides arises from reports of the occurrence of PLC or PLEVA in the setting of infection (eg, Toxoplasma gondii, Epstein-Barr virus, parvovirus B16, human immunodeficiency virus, staphylococci, Group A streptococci, others) [2,8-11]. In addition, the relatively young age of onset and an observation of a familial outbreak of PLEVA have led some authors to propose infection as a trigger for pityriasis lichenoides [2,12].
The theory that PLC is a primary lymphoproliferative disease is based upon studies demonstrating clonal CD4+ T cell populations in tissue samples from patients with PLC and PLEVA [13,14]. However, monoclonality is not uniformly detected in PLC; in one study, only 1 of 13 PLC specimens demonstrated a monoclonal T-cell receptor gene rearrangement . Moreover, the detection of monoclonality is not sufficient to designate a disorder as a primary lymphoproliferative disease .
Occasionally, PLC has been reported to occur in association with drug exposure [16-18]. The mechanisms through which drugs might induce PLC are unknown.
CLINICAL FEATURES — The development of pityriasis lichenoides chronica (PLC) usually is gradual. Patients develop numerous red-brown papules that often demonstrate a characteristic overlying mica-like scale (picture 1A-C). Lesions in different stages of development are present simultaneously.
The trunk, buttocks, and proximal extremities are the most common sites of involvement. However, other cutaneous areas may be affected. Although the eruption usually is asymptomatic, associated pruritus occurs in some patients.
Patients with PLC typically exhibit a relapsing and remitting disease course that lasts for months to years. In a retrospective study of 46 children with PLC, the median duration of disease was 20 months (range 3 to 132 months) . Individual lesions heal over several weeks leaving hypopigmented or hyperpigmented macules or patches . Scarring is absent. Occasionally, patients present with widespread hypopigmented macules as the predominant clinical manifestation of the disease (picture 2) [19,20].
HISTOPATHOLOGY — Compared with pityriasis lichenoides et varioliformis acuta (PLEVA), the pathologic findings of pityriasis lichenoides chronica (PLC) are less pronounced. (See "Pityriasis lichenoides et varioliformis acuta (PLEVA)", section on 'Histopathology'.)
The characteristic pathologic features of PLC include :
DIAGNOSIS — A diagnosis of pityriasis lichenoides chronica (PLC) is usually suspected based upon the clinical appearance. We typically perform a skin biopsy to confirm the diagnosis.
A 4 mm punch biopsy of a papule usually provides a specimen that is sufficient for the histologic evaluation for PLC. (See 'Histopathology' above and "Skin biopsy techniques", section on 'Punch biopsy'.)
DIFFERENTIAL DIAGNOSIS — The differential diagnosis of pityriasis lichenoides chronica (PLC) includes other disorders that may present with widespread papules or small plaques. A skin biopsy often is useful for distinguishing PLC from other diseases.
Examples of disorders that may resemble PLC include:
Approach to treatment — Because pityriasis lichenoides chronica (PLC) is a benign, nonscarring condition that is often asymptomatic and self-limited, treatment is not mandatory. However, we find that many patients desire therapy to improve the visible signs of the disease.
The best approach to treatment is unclear due to a paucity of high quality efficacy data. Sources of data are primarily limited to case reports and retrospective studies. Moreover, many studies have combined outcome data from patients with PLC and pityriasis lichenoides et varioliformis acuta (PLEVA), complicating interpretation of treatment efficacy for patients with PLC.
Given the lack of high quality data on treatment efficacy and the benign course of PLC, the risks associated with pursuing treatment should always be considered carefully. Our initial approach to treatment consists of therapies that have been reported to be effective and have a favorable safety profile. We favor topical corticosteroids and oral antibiotics with antiinflammatory properties for first-line therapy for PLC and consider phototherapy an additional treatment option. Because of concern for serious drug side effects, we reserve treatment with methotrexate and other systemic immunomodulatory therapies for patients with severe and refractory disease.
First-line therapy — Topical corticosteroids and oral antibiotics are our first-line treatments for PLC.
Topical corticosteroids — Topical corticosteroids are commonly used for PLC despite little published data on their efficacy. These agents may be useful for improving inflammation and reducing associated pruritus. In a retrospective review that included 18 adults and 16 children with PLEVA or PLC who received topical corticosteroid therapy, approximately one-half found the treatment useful for clearing or virtually clearing symptoms or signs of the disease . We typically prescribe a medium potency topical corticosteroid (eg, triamcinolone 0.1% cream) to be applied twice daily for four to six weeks to sites of active lesions.
Cutaneous atrophy is a potential adverse effect of topical corticosteroid use that is most likely to occur with long-term use of high potency corticosteroids. Additional side effects of topical corticosteroids, including the effects of systemic absorption, are reviewed separately. (See "General principles of dermatologic therapy and topical corticosteroid use", section on 'Side effects'.)
Oral antibiotics — Oral antibiotics with antiinflammatory properties may be useful for the management of PLC and are commonly used as first-line therapy. In particular, patients with widespread eruptions may prefer oral therapy over topical therapy due to the difficulty of applying a topical agent to multiple areas.
Tetracyclines and erythromycin are the oral antibiotics most commonly used for PLC. Tetracyclines are typically used for the treatment of adolescents and adults. Tetracyclines should not be given to children under the age of nine or pregnant women due to the risk for permanent discoloration of developing teeth. Thus, erythromycin is typically used for the treatment of children with PLC.
Improvement with oral antibiotic therapy is usually evident within the first several weeks of treatment. If benefit is not evident within three months, we discontinue the oral antibiotic and consider initiating phototherapy.
Tetracyclines — The efficacy of tetracycline was evaluated in an uncontrolled study of 13 patients with pityriasis lichenoides (subtype unspecified) . Patients were treated with 2 g per day of tetracycline until lesions subsided followed by 1 g per day for one month. Of the 13 patients, 12 achieved marked improvement within four weeks. Seven patients needed to continue tetracycline (1 g per day) to maintain the response to treatment.
Favorable results following treatment with a tetracycline class antibiotic were also reported in a separate retrospective study. Three of four adults treated for pityriasis lichenoides (subtype unspecified) with minocycline (100 mg twice daily for eight weeks) achieved clearance or near clearance of skin lesions .
Our typical regimen of tetracyclines for adults consists of one of the following:
Gastrointestinal distress is a potential side effect of these antibiotics. In addition, tetracyclines (particularly tetracycline and doxycycline) may induce photosensitivity. Uncommon side effects of minocycline include skin pigmentation and a lupus-like syndrome.
Erythromycin — The findings of several retrospective studies in children with pityriasis lichenoides suggest that oral erythromycin may be beneficial in this population [4,5,7,23]. Most studies have not separated outcomes for patients with PLC from those with PLEVA.
However, not all studies have yielded a high rate of response. A retrospective study of eight children with pityriasis lichenoides (type unspecified) treated with erythromycin (40 to 60 mg/kg per day) found that only two children achieved clearance after three months of treatment, one of whom relapsed within four weeks of treatment cessation .
The dose of erythromycin that we typically use for children is 30 to 50 mg/kg per day. Gastrointestinal distress is a potential side effect of erythromycin therapy.
Azithromycin, another macrolide antibiotic, has been reported to be effective in a few patients with PLEVA [24,25]. The efficacy of azithromycin for PLC is unclear. (See "Pityriasis lichenoides et varioliformis acuta (PLEVA)", section on 'Azithromycin'.)
Second-line therapy — Phototherapy is a well-tolerated modality that may be beneficial for PLC. Phototherapy is easily administered to a wide area of skin, a favorable feature for patients with widespread involvement. However, the multiple office visits required make phototherapy a less feasible treatment option for some patients.
Phototherapy — Small uncontrolled studies, retrospective studies, and case reports offer support for the use of phototherapy for PLC and PLEVA [2,26]. Narrowband UVB, broadband UVB, and PUVA are the primary phototherapeutic modalities used to treat these diseases. (See "UVB therapy (broadband and narrowband)" and "Psoralen plus ultraviolet A (PUVA) photochemotherapy".)
Efficacy — Several uncontrolled and retrospective studies have evaluated the efficacy of UVB phototherapy for PLC, with most studies reporting improvement in the majority of patients [26-31]. One of the largest retrospective studies of narrowband UVB phototherapy in patients with PLC (n = 25, Fitzpatrick skin phototype II or III (table 1)) documented complete (>75 percent improvement) and partial (50 to 75 percent improvement) responses in 48 and 44 percent of patients, respectively . In a separate retrospective study that included eight patients with PLC (Fitzpatrick skin phototype I or II) who were treated with narrowband UVB, seven (88 percent) achieved a complete response (at least 90 percent clearance of skin lesions) and one patient achieved a partial response (50 to 89 percent clearance of lesions) .
Few studies have directly compared the efficacy of different forms of phototherapy for PLC. Similar efficacy of narrowband UVB and PUVA was suggested by an unblinded trial in which 15 patients with PLC were randomly assigned to either treatment . The trial did not find a significant difference in the rate of response to therapy; 88 percent of narrowband UVB-treated patients and 74 percent of PUVA-treated patients achieved more than 90 percent resolution of papulosquamous and plaque lesions and the mean number of treatment sessions required to achieve this response was similar. In addition, a retrospective study that compared narrowband UVB to broadband UVB therapy in 29 patients with pityriasis lichenoides (PLEVA, PLC, or an overlap syndrome) found a similar rate of response . Complete clearance of lesions was achieved by 93 percent of patients in both groups.
UVA1 phototherapy is not widely available and experience with this modality for PLC is limited. In a prospective study, treatment with UVA1 was associated with complete clinical and histologic improvement in six of eight patients with PLC or PLEVA .
Administration — At least two to three months of treatment is usually required to achieve good responses to UVB and PUVA phototherapy. Treatment often is initially administered at least three times weekly and tapered to less frequent treatments once there is a satisfactory response. Relapse may occur after the discontinuation of treatment.
Potential adverse effects of UVB and PUVA phototherapy include blistering, burns, and pruritus. Increased risk for squamous cell carcinoma has been reported in psoriasis patients who have received high numbers of PUVA treatments . The adverse effects of phototherapy are reviewed in greater detail separately. (See "UVB therapy (broadband and narrowband)", section on 'Short- and long-term adverse effects' and "Psoralen plus ultraviolet A (PUVA) photochemotherapy", section on 'Adverse effects'.)
Additional therapies — There are few data on additional treatment options for PLC.
Topical tacrolimus — A few case reports suggest that topical tacrolimus may be an additional topical treatment option for pityriasis lichenoides. Improvement of longstanding PLC that failed to respond sufficiently to topical clobetasol, oral erythromycin, phototherapy, or methotrexate was documented in a patient in whom lesions on one side of the body were treated with tacrolimus 0.1% ointment twice daily . Although marked improvement was noted within two weeks, lesions recurred soon after treatment cessation. Topical tacrolimus also appeared to be useful in two children with PLEVA . Additional studies will be useful for confirming the efficacy of topical tacrolimus for PLC.
Transient stinging or burning sensations may occur at sites of tacrolimus application. Although some safety concerns have been raised regarding the risk for lymphoma in patients treated with topical tacrolimus, a causative relationship has not been proven. (See "Treatment of atopic dermatitis (eczema)", section on 'Long-term safety concerns'.)
Methotrexate — Case reports have documented efficacy of methotrexate treatment in a few patients with PLC, including patients with PLC that appeared to be induced by treatment with a biologic TNF-alpha inhibitor [16,37,38]. Methotrexate has also been used successfully for the treatment of PLEVA and febrile ulceronecrotic Mucha-Habermann disease (FUMHD). (See "Pityriasis lichenoides et varioliformis acuta (PLEVA)", section on 'Refractory disease'.)
Due to the benign clinical course of PLC and the potential side effects of methotrexate, our use of methotrexate is infrequent. We primarily reserve methotrexate therapy for patients with extensive or symptomatic PLC who have failed other therapies. The side effects of methotrexate are reviewed separately. (See "Major side effects of low-dose methotrexate".)
Other — Treatment with other systemic therapies such as dapsone, acitretin with PUVA, systemic glucocorticoids, cyclosporine, and intravenous immunoglobulin have been suggested for the treatment of refractory PLEVA or FUMHD based upon isolated reports of benefit [2,39-42]. The efficacy of these agents in PLC is unclear. The risks of treatment should be carefully considered prior to attempting treatment with such agents. A response to photodynamic therapy has been reported in one patient with PLC .
ASSOCIATION WITH MALIGNANCY — The development of cutaneous lymphoma, most commonly mycosis fungoides, has been reported in several children and adults with pityriasis lichenoides chronica (PLC) [13,44-48]. In addition, two patients in whom PLC appeared to be a paraneoplastic phenomenon related to a renal oncocytoma or an extranodal lymphoma have been reported [47,49]. (See "Clinical manifestations, pathologic features, and diagnosis of mycosis fungoides", section on 'Clinical features'.)
Given the apparent rarity of associations between PLC and malignancy, PLC is considered a benign disease. However, as a precaution, we perform a full skin examination on patients with PLC at least once yearly to evaluate for signs of cutaneous lymphoma. We also encourage patients to return if atypical skin lesions develop (eg, persistent inflammatory patches, plaques, or tumor-like nodules). We do not routinely perform cancer screening beyond recommended age-appropriate measures.
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