Pityriasis lichenoides chronica: case reports – the role of infectious agents?

Introduction

Pityriasis lichenoides chronica (PLC), which is a benign eruption with lymphocytic infiltrates of the skin, presents as a persistent, erythematous, papular eruption with scale. Patients may have guttate, hypopigmented macules with scale in addition to papules [1]. It is related histopathologically to pityriasis lichenoides et varioliformis acuta (PLEVA), which presents as a recurrent papulonecrotic eruption.
The PLC is a cutaneous disease of unknown etiology that most commonly affects children and young adults. The highly variable presentation of this condition often poses a diagnostic challenge.

Objective

We present two cases of pityriasis lichenoides chronica probably induced by group A b-hemolytic Streptococcus in one case and by Trichomonas vaginalis in the other.

Case reports

Patient 1

A 45-year-old woman presented with scaly, pruritic, erythematous-to-brown flattened papules, which varied in size from 3 mm to 1 cm, on the trunk and extremities, being first diagnosed as guttate psoriasis (Figs. 1 A and B). The close view of the lesions showed fine centrally attached mica-like shiny scales, which raised the suspicion of pityriasis lichenoides chronica.
Laboratory findings were within normal limits, with the exception of the evidence of group A b-hemolytic Streptococcus in throat swab cultures and antistreptolysin-O (ASO) antibody titers over normal value (500 UI/ml).
The histopathological report confirmed the suspicion of pityriasis lichenoides chronica (Figs. 2 A and B).
Immunohistochemistry: CD 20 was negative in the inflammatory infiltrate and CD 45 was strongly positive.
Antibiotic therapy was started, with macrolides for 10 days, followed by 4 administration of dibenzylethylenediamine-dipenicillin G 1.2 million/week and phototherapy (narrow-band UVB) for 2 weeks.
The evolution was favorable, with persistent minimal residual hyperpigmentations and discrete xerosis. The laboratory investigations returned to normal values within 1 month and the patient was not followed up.

Patient 2

A 28-year-old male patient sought medical advice for a disseminated eruption on the trunk and extremities, observed 2 months before the consultation (Fig. 3). He was in a good medical state, with no comorbidities and no medication. He complained of discrete pruritus and urethral discharge for many days.
The urethral smear evidenced Trichomonas vaginalis (Giemsa-stained smears and culture).
A punch biopsy was taken from a fresh papule from the left limb and the suspicion of pityriasis lichenoides chronica was kept in mind.
Based on clinical and histopathological results (Figs. 4 A and B), a diagnosis of pityriasis lichenoides chronica was established and treatment with topical steroids class II and tinidazole 1 γ daily for 5 days orally was recommended. The skin lesions disappeared in approximately one month, with no recurrences.

Discussion

Pityriasis lichenoides is a disease of unknown origin. Older studies supported an immune complex pathogenesis, whereas more recent studies suggest that it is a lymphoproliferative disorder, probably triggered by an antigenic stimulus, such as a virus or other infectious agent.
The pathognomonic lesion is an erythematous papule that develops a reddish brown hue and a centrally adherent micaceous scale, that can easily be detached, to reveal a shiny, pinkish brown surface. The papule spontaneously flattens and regresses over a period of weeks. It often leaves a hyper- or hypo-pigmented macule [2, 3]. The entire course of an eruption can take several years and, very often, lesions may be present in all stages of development [4]. pityriasis lichenoides chronica usually occurs on the trunk and proximal parts of the extremities, but acral and segmental distributions have also been described, the lesions being usually asymptomatic.
Infectious agents have long been suspected as etiologic factors in this disease and many reports from the literature link pityriasis lichenoides chronica with various pathogens in genetically susceptible individuals [5]: HIV, varicella-zoster virus, Epstein-Barr virus (EBV), cytomegalovirus [6], parvovirus B19 [7], adenovirus, Staphylococcus, Streptococcus [8], herpes virus [9], Mycoplasma, chronic hepatitis C virus [10] and Toxoplasma. The PLC in association with human immunodeficiency virus infection has been reported and improves with the rise in CD4 count. The EBV has been associated with PLEVA outbreaks, and PLC was associated with a fulminant case of infectious mononucleosis, which resolved with resolution of the EBV and treatment with narrow-band ultraviolet B phototherapy. Toxoplasma was reported in PLC in 1972 in 6 of 11 patients. Other infectious agents that have been implicated as causing PLC include adenovirus and parvovirus B19. Niemczyk et al. described a case of a child with a history of previous infection, in which pneumococci and Haemophilus influenzae were isolated [11].
The evidence that bacterial infection could be contributory to the pathogenesis of pityriasis lichenoides chronica is suggested by the successful use of antibiotics such as erythromycin and tetracycline. Piamphongsant in his study on 13 patients with PLC could isolate coagulase-positive staphylococci in 4 patients in their throat swab cultures [12]. Other bacteria including coagulase-negative staphylococci, B streptococci, Streptococcus pneumoniae and Pseudomonas aeruginosa were also isolated in other patients. Most of his patients showed a good clinical response to tetracycline therapy.
We have described two cases of pityriasis lichenoides chronica with typical lesions, induced (or triggered) by group A b-hemolytic Streptococcus and Trichomonas vaginalis.
Pityriasis lichenoides may have arisen secondarily to these infectious or there were two simultaneous diseases. Further studies must elucidate the role of infectious agents in this pathology.

References

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12. Piamphongsant T.: Tetracycline for the treatment of pityriasis lichenoides. Br J Dermatol 1974, 91, 319-326.

Otrzymano: 4 III 2014 r.
Zaakceptowano: 5 V 2014 r.