Red Bumps on Arms and Legs

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A 6-year-old girl presents with a 1-year history of a waxing and waning rash on her limbs and face. The rash starts as red scaly bumps that fade over several weeks leaving smooth white spots. Every few months, the patient gets several new red bumps. The rash is not itchy or painful. Her parents have tried topical steroid creams that did not help clear the rash. Examination reveals scattered erythematous scaly papules on both legs and several hypopigmented macules on her legs, arms, and face.

Pityriasis lichenoides (PL) describes a spectrum of acute and chronic dermatoses that includes pityriasis lichenoides et varioliformis acuta (PLEVA) and pityriasis lichenoides chronica (PLC).1,2 The chronic form, PLC, is characterized by scaly red to brown papules that resolve spontaneously and...

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Pityriasis lichenoides (PL) describes a spectrum of acute and chronic dermatoses that includes pityriasis lichenoides et varioliformis acuta (PLEVA) and pityriasis lichenoides chronica (PLC).1,2 The chronic form, PLC, is characterized by scaly red to brown papules that resolve spontaneously and recur frequently.1,2

In 1894, the chronic and acute forms of PL were first described by Jadassohn and Neisser, respectively, in separate case reports.3-5 The term pityriasis lichenoides chronica was first used in 1899 by Juliusberg.3,6 The acute form of PL was distinguished from PLC in 1916 by Mucha7 and was named pityriasis lichenoides et varioliformis acuta in 1925 by Habermann.3,7

The prevalence of PL in the general population is estimated to be 0.05%.1 It is slightly more common in men and occurs more frequently in late childhood or early adulthood, but can occur at any age.3 Pityriasis lichenoides has been reported across many ethnic groups and geographic locations with no racial predilection.1,3,8 The PLC subtype occurs more frequently than PLEVA and tends to affect children.1,3,8 One study found that Black patients were more likely to develop PLC and White patients were more likely to develop PLEVA.9

Although the exact etiology and pathogenesis of PL are not understood fully, 3 theories predominate.8 The first theory is that PL is an inflammatory reaction to an antigenic agent. Infections and drugs have been linked to cases of PL.3,8 An infectious etiology is supported by several characteristics of PL such as familial outbreaks, young age of onset, and acute eruptions. Infectious PL cases have been linked to Toxoplasma gondii, Epstein-Barr virus, and HIV.3 The second theory is that PL is a lymphoproliferative disorder. This theory is supported by reported cases of PLC progressing to mycosis fungoides.8 The third major etiologic theory states that PL is an immune-complex–mediated hypersensitivity vasculitis.3,8 Studies have found immunoglobin deposits in biopsies of PL lesions and circulating immune complexes in some patients with PL.8

PLC typically presents with gradually developing lesions on the proximal extremities and trunk. The lesions are small, erythematous or brown, and have centrally attached fine parakeratotic scales.2,8 When removed, these scales may leave a shiny brown or pink macule.8 The lesions generally do not scar but leave areas of hyper- or hypopigmentation. Patients with PLC may experience periods of remission between outbreaks.1,2

The distribution of lesions can predict the disease course; peripheral PLC lesions can take years to fade, whereas a generalized rash tends to resolve more quickly.2 Compared with PLEVA, PLC has a more indolent course and lacks epidermal necrosis. The lesions also can present concurrently with PLEVA lesions or after PLEVA lesions subside.3,8 Fever and pruritus rarely occur in PL.8  The histopathology of PL shows epidermal parakeratosis, dermal edema, necrotic keratinocytes, lichenoid inflammation, and perivascular lymphohistiocytic inflammatory infiltrate. In PLC, the lymphocytic perivascular infiltrate tends to be sparse, superficial, and dominated by CD4+ T cells.8 Rarer histologic findings in PLC include hemorrhage, spongiosis, neutrophilic infiltrate, epidermal vesicle formation, dyskeratosis, and basilar vacuolar changes.2,8

The condition is diagnosed by clinical presentation correlated with histologic findings.3,8 A full workup may be needed to exclude other diagnoses. Depending on clinical presentation, complete blood cell count and serologic tests for T gondii, herpes simplex virus, HIV, Epstein-Barr virus, and cytomegalovirus may be useful.8

One condition that can be confused with PLC and PLEVA is lymphomatoid papulosis.3 This disease, however, will show different histologic findings than PL and, unlike PL, it is characterized by overexpression of CD30+ atypical T cells.3,8  The differential diagnosis should also include lichen planus, guttate psoriasis, pityriasis rosea, secondary syphilis, and viral or drug exanthems.3,8 These conditions usually can be differentiated from PL via clinical and histologic findings.3,8 Laboratory tests such as venereal disease research laboratory test, immunopathologic evaluation, antistreptolysin O titers, and throat cultures can assist in differential diagnosis.3

Although some cases of PL spontaneously resolve over several weeks, other cases persist for years. The condition is relatively benign, but treatment for PLC may be pursued because of cosmetic concerns and for symptomatic relief.1,8 Oral antibiotics such as azithromycin, erythromycin, and tetracycline are considered first-line treatments. Antibiotic doses must be tapered gradually to prevent recurrence. Topical corticosteroids may be used in conjunction with antibiotics to offer symptomatic relief of pruritus and inflammation.8 Phototherapy with narrowband UV-B has shown success.1,8 Severe PL cases may warrant use of methotrexate, cyclosporine, dapsone, or acitretin.8

The patient in this case had a punch biopsy of a lesion on the lower extremity that confirmed a diagnosis of PLC. She is being treated with a 3-month course of erythromycin, which she is tolerating well.

antibiotics, but administration of a different cephalosporin typically is well-tolerated.13 Patients who have had SSLR induced by minocycline should consider avoiding other tetracyclines because little is known about cross-reactivity.13 

The patient in this case was treated in the ED with antihistamines and topical steroids. He showed significant improvement in his rash overnight and then resolution over the next week. He has experienced neither sequelae from the rash nor recurrence.

Dina Zamil, BS, is a medical student at Baylor College of Medicine, in Houston, Texas; Tara L. Braun, MD, is a resident in the Department of Dermatology at Baylor College of Medicine; and Christopher Rizk, MD, is a dermatologist affiliated with Baylor College of Medicine.

References

1. Jung F, Sibbald C, Bohdanowicz M, Ingram JR, Piguet V. Systematic review of the efficacies and adverse effects of treatments for pityriasis lichenoides. Br J Dermatol. 2020;183(6):1026-1032. doi:10.1111/bjd.18977

2. Khachemoune A, Blyumin ML. Pityriasis lichenoides: pathophysiology, classification, and treatment. Am J Clin Dermatol. 2007;8(1):29-36. doi:10.2165/00128071-200708010-00004

3. Bowers S, Warshaw EM. Pityriasis lichenoides and its subtypes. J Am Acad Dermatol. 2006;55(4):557-572; quiz 573-576. doi:10.1016/j.jaad.2005.07.058

4. Jadassohn J. Ube rein eingenartiges psoriasiformes und lichenoides Exanthem. Verh Dtsch Dermatol Ges. 1894;4:524-529.

5. Neisser A. Zur Frage der lichenoiden Eruptionen. Verh Dtsch Dermatol Ges. 1894;4:495-499.

6. Juliusberg F. Uber die Pityriasis lichenoides chronica (psoriasiform exanthem). Arch Dermatol Syphilol. 1899;50:359-374.

7. Mucha V. Uber einen der Parakeratosis variegata (Unna) bzw. Pityriasis lichenoides chronica (Neisser-Juliusberg) nahestehenden eigentumlichen Fall. Arch Dermatol Syph. 1916;123:586-592.

8. Moy A, Sun J, Ma S, Seminario-Vidal L. Lymphomatoid papulosis and other lymphoma-like diseases. Dermatol Clin. 2019;37(4):471-482. doi:10.1016/j.det.2019.05.005

9. Zang JB, Coates SJ, Huang J, Vonderheid EC, Cohen BA. Pityriasis lichenoides: long-term follow-up study. Pediatr Dermatol. 2018;35(2):213-219. doi:10.1111/pde.13396

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