Pityriasis lichenoides chronica (PLC) is a benign, self-limited, diffuse skin eruption composed of discrete red–brown scaly papules (Fig. 37-1). In darker-skinned patients, PLC may present instead with hypopigmented nonscaly macules and patches (Fig. 37-2).¹ Individual lesions typically last from weeks to several months, whereas the eruption persists from months to years in a given patient. PLC is thought to be closely related to a more severe condition, pityriasis lichenoides et varioliformis acuta (PLEVA), also known as Mucha–Habermann disease, and in fact may evolve from this more acute form. It may also arise independently of a preceding PLEVA eruption. Similar to PLEVA/Mucha–Habermann disease, an individual patient affected with PLC often has lesions in all stages of development, from those that are newly erupted to those that are in the resolution phase.

The lesions of PLC are most often diffusely distributed on the trunk and proximal extremities; however, segmental and acral presentations of this condition have been described.² The lesions are usually asymptomatic, although rarely patients complain of pruritus. PLC affects both children and adults. The incidence in women and men appears to be equal, without a predilection for one gender.²

PLC is felt to be an indolent condition. Progression from PLC to cutaneous lymphoma has been documented in the literature, but this occurs rarely.^3,4 Resolution of the lesions, which may be spontaneous or aided by the use of topical or systemic medications, typically results in dyspigmentation, either hypo- or hyperpigmentation⁵; scarring is not commonly seen. Interestingly, it has been suggested in the literature that children with PLC tend to have a more difficult course as compared to adults, with higher lesion counts and a greater degree of dyspigmentation.⁶ In addition, children may not be as responsive to therapy.

Occasionally, PLC has been reported to arise following use of systemic medications, including the TNF-α inhibitors adalimumab and infliximab.^7,8,9 PLC has also been associated with viral infections, including HIV and HHV-8.^10,11

Several therapeutic options exist for the treatment of PLC. Patients may be successfully treated with mid-to-high–potency topical steroids. The topical calcineurin inhibitor tacrolimus has also been reported to be effective for cases of PLC, at concentrations of 0.03% and 0.1%, and is particularly useful when a steroid-sparing agent is desired.^10,11

Ultraviolet light therapy is generally efficacious in the treatment of PLC. A small study of narrow-band ultraviolet B (nbUVB) and psoralen plus ultraviolet A (PUVA) light therapy in patients with pityriasis lichenoides found that out of eight patients treated with nbUVB seven had a complete response to therapy and one had a partial response (the mean number of treatment sessions was 37), whereas out of seven PUVA-treated patients five had a complete response and two had a partial response (the mean number of treatment session was 40).¹²

Oral medications commonly used for the treatment of PLC include systemic antibiotics and methotrexate. Macrolide antibiotics including erythromycin and azithromycin as well as tetracycline are commonly utilized in this setting for their anti-inflammatory rather than antimicrobial properties. For children, erythromycin is the preferred treatment over tetracycline, as tetracycline dosing is contraindicated in children younger than 8 years out of concern for its adverse effects on secondary tooth development. Hapa et al.¹³ recently suggested that treatment duration for erythromycin should be at least 3 months, on the basis of their finding that treatment response rates improved to 83% in month 3 of therapy, compared to 64% and 73% in months 1 and 2, respectively.