Are You Confident of the Diagnosis?

What you should be alert for in the history

Pityriasis lichenoides chronica (PLC) is rarely as symptomatic as it is alarming. When this form of parapsoriasis was being described in the literature it was grouped under the “rhythmic eruptions” due to the unexplainable eruption of multiple lesions followed by the gradual involution and fading of that crop. Given the lack of symptoms, many patients tend to ignore it and given the disease’s natural history of spontaneous involution their wishes tend to be fulfilled—it goes away. Thus, a history of a rhythmic eruption that fades is a key finding in the history. In addition, the lesions tend to disappear with sunlight exposure, so the face and repetitively sun-drenched areas of the skin tend to escape the rhythmic eruption while truncal and proximal extremity lesions dominate.

Characteristic findings on physical examination

One key feature of PLC that aids in is differentiation from mycosis fungoides is the monomorphic nature of the lesions and their synchronous distribution in time (Figure 1). Individual lesions vary in size from 4-40 mm with an oval papulosquamous primary lesion. The long axes of the oval lesions tend to be parallel. One characteristic place to see a string-of -beads–like configuration of these lesions is around the axilla or inguinal region. On the back a “Christmas tree” like configuration can also arise from parallel oval lesions draping down and away from the spine (the tree trunk).

Figure 1.

The lesions of PLC show a monotonous morphology of roughly the same-sized lesions on a given patient as shown here on the thigh.

Expected results of diagnostic studies

The most surprising finding on biopsy is that if the pathologist is not aware of this being a monomorphous eruption of small papules, the pathology may be interpreted as being suspicious of mycosis fungoides. Typically there is a patchy lichenoid infiltrate that is very focal with overlying parakeratosis. Epidermotropic lymphocytes are not unusual. If the suspicion of mycosis fungoides is pursued the next surprising finding is that there often is T-cell clonality by molecular studies. These are the characteristic features of this benign relapsing rhythmic eruption.

If the clinical and pathologic features are not classic for PLC, immunochemistry may be useful in that CD8+ infiltrates are common and the lesions are clinically distinct from other CD8+ infiltrates, such as cytotoxic cutaneous T-cell lymphoma and varicella infection. .No serology or imaging tests are indicated. However, all patients need a thorough skin examination, which should be repeated periodically as long as the condition is active.

Diagnosis confirmation

The clinical and pathological correlation typically suffice for the diagnosis. However, there are two eruptions that can mimic PLC and to some degree overlap with it. One is the more virulent and scarring rhythmic eruption of lymphomatoid papulosis. The other is the pityriasis rosea-like drug eruptions. The latter tend not to be as well organized as the classic case of PLC but the history should still be scoured for exposure to imatinib, anti-tumor necrosis factor inhibitors, angiotensin converting enzyme inhibitors, terbinifine, and gold therapy.

Who is at Risk for Developing this Disease?

PLC has been reported in patients ranging from from neonates to octagenarians.

What is the Cause of the Disease?

There is no known cause. As a fairly common condition, there have been numerous hints of this eruption being associated with the common viruses human herpes virus 6 and 7, Parvo virus, and Epstein-Barr Virus. There is not enough of an association to warrant serologic studies or antiviral therapy.

Systemic Implications and Complications

There have been several cases reported of mycosis fungoides appearing in patients who exhibited PLC. In addition, it is not unheard of for patients with mycosis fungoides to exhibit PLC lesions in the background of their other cutaneous lesions. PLC is not a lymphoma precursor. The scattered case reports do reinforce the need for periodic skin exams, mainly to look for the characteristic lesions of mycosis fungoides.If the skin exam is negative, no studies for cutaneous lymphoma are indicated.

The major complication of the disease is cosmetic. With the lichenoid inflammation there is often post inflammatory hyperpigmentation in skin of color. Unlike lighter skinned patients where lesions leave without any trace, a patient with skin of color is often left with persistent reminders of previous outbreaks

Treatment Options

Wait and Watch

This is probably the most commonly used approach, since many patients do this at home before and after seeing a dermatologist. A thorough understanding of the benign rhythmic nature of the disease is critical for the patient to put up with the recurring outbreaks.


In order of ease of administration and patient acceptability it is not unusual to utilize phototherapy to clear up old lesions and inhibit the development of new ones for a given period of time. Obviously a patient could not continue multiple photoptherapy sessions per week for life, but long remissions can be achieved from a 2-3 month course of treatment. Tanning parlors are often the modality of choice for patient convenience and expense. Narrow-band ultraviolet B therapy at 2-3 sessions per week can usually remit the disease over a course of 20-30 sessions.

Systemic Therapy

This safest therapy touted for PLC is also the least reliable, but worth pursuing due to the benign nature of the drugs: antibiotics at acne doses and durations. The macrolides erythromycin, azithromycin, and clarithromycin at doses of 250mg to 500mg per day for at least 2 months have been the most popular. Tetracycline and its derivatives have also been used at the same doses used for acne; however, given the tendency to utilize phototherapy and for the eruption to appear in children, these antibiotics tend to be prescribed less often.

The most reliable systemic therapy for PLC is weekly methotrexate at doses similar to those successful for psoriasis. One unique feature of PLC is that once controlled with methotrexate the dose can often be reduced to 5mg per week to suppress new crops from appearing. Again, the benign nature of the disease must balance any risk of hepatotoxicity or bone marrow suppression.

Optimal Therapeutic Approach for this Disease

Almost all patients undergo a course of antibiotics, given the ease of administration and lack of need for laboratory monitoring of this treatment. Azithromycin 250mg per day is a well-tolerated dose. The major factor complicating any efficacy assessment is the remitting nature of the disease. If the patient clears after a month it would be prudent to claim victory and wait for the next outbreak before any more antibiotic is dispensed. If there is no response, 1 to 2 months is adequate time to determine treatment failure. At that point, a symptomatic patient should be considered for either phototherapy or weekly methotrexate depending on comorbidities, age, and availability.

Patient Management

On the initial visit, the differential diagnosis is explained to the patient, along with the need for biopsy diagnosis. A punch biopsy is needed to see the bottom of the often wedged-shaped infiltrate. On the second visit the benign rhythmic nature of the condition is explained to the patient, along with the concept that therapy is dictated by symptoms. If any therapy is begun, a clear time point should be chosen when the decision will be made whether or not therapy is effective.

If the patient achieves clearing, it is worthwhile explaining that the intervals between outbreaks will be very important to monitor, as everyone has a different rhythm. A diary of some type would suffice. Should no therapy be selected or no therapy is successful (methotrexate is almost always successful) then the patient still needs to come in twice a year for a good skin exam, a discussion of advances in PLC, and a discussion of any change in strategy.

Unusual Clinical Scenarios to Consider in Patient Management

The unusual clinical scenario one might encounter is a patient who has undergone a stem cell transplant for some type of hematologic malignancy. In that setting, the clinical and pathological features of PLC would be interpreted as a form of chronic graft-versus-host disease. This observation is useful in trying to answer the PLC patient’s question about “what causes this”? In the setting of a transplant, we know the cause. But in the wild-type form of the disease, we can only speculate it is a similar relapsing/remitting misguided inflammatory response.

What is the Evidence?

Khachemoune, A, Blyumin, ML. “Pityriasis lichenoides: pathophysiology, classification, and treatment”. Am J Clin Dermatol. vol. 8. 2007. pp. 29-36. (In this review, the histologic features that characterize PLC and differentiate it from the acute form are reviewed.)

Ersoy-Evans, S, Greco, MF, Mancini, AJ, Subasi, N, Paller, AS. “Pityriasis lichenoides in childhood: a retrospective review of 124 patients”. J Am Acad Dermatol. vol. 56. 2007. pp. 205-10. (Pityriasis lichenoides chronica is one of the most common forms of parapsoriasis in children. This review provides a broad view of the clinical spectrum in the pediatric population. Also, the treatment of children is slightly different from that of adults, with an emphasis on antibiotics.)

Lam, J, Pope, E. “Pediatric pityriasis lichenoides and cutaneous T-cell lymphoma”. Curr Opin Pediatr. vol. 19. 2007. pp. 441-5. (This review includes data from the pediatric registry of cutaneous lymphomas. The rare associations of pityriasis lichenoides with lymphomas are reviewed.)

Truhan, AP, Hebert, AA, Esterly, NB. “Pityriasis lichenoides in children: therapeutic response to erythromycin”. J Am Acad Dermatol. vol. 15. 1986 Jul. pp. 66-70. (The classic paper that put antibiotic therapy at the forefront of pityriasis lichenoides management.)

Ersoy-Evans, S, Hapa, AA, Boztepe, G, Sahin, S, Kölemen, F. “Narrowband ultraviolet-B phototherapy in pityriasis lichenoides chronica”. J Dermatolog Treat. vol. 20. 2009. pp. 109-13. (With the declining use of photochemotherapy, narrowband has become the most available office-based phototherapy for pityriasis lichenoides. While patients can often be cleared, the real benefit is in prolongation of intervals between the courses of phototherapy.)

Lynch, PJ, Saied, NK. “Methotrexate treatment of pityriasis lichenoides and lymphomatoid papulosis”. Cutis. vol. 23. 1979 May. pp. 634-6. (Weekly methotrexate has become a reliable modality for controlling pityriasis lichenoides when symptoms and signs disrupt the patient’s quality of life.)