Pityriasis rosea
Introduction
Pityriasis rosea is an acute,
self-limiting papulosquamous disease, probably
viral in origin, affecting mainly children and young adults, and characterized
by a distinctive skin eruption and minimal constitutional symptoms.
Epidemiology
Most cases of
pityriasis rosea occur between the ages of 10 and 35 years and the disease is
most prevalent in the spring and autumn. It is slightly more common in females.
Pathogenesis
Involvement of two
herpes viruses, HHV-6 and HHV-7, has been suggested as a cause for the
eruption. The viral DNA is reported to be present in the PBMCs and lesional and
unaffected skin of the majority of individuals with acute pityriasis rosea. The
natural history of the disease, with a primary lesion which could correspond to
the site of inoculation, a disseminated secondary eruption after an interval,
mild constitutional symptoms, a self-limiting course, and the infrequency of
second attacks, are all features of viral origin. Many drugs can cause
pityriasis rosea-like eruptions and include metronidazole, barbiturates,
clonidine, captopril, ketotifen, adalimumab,
angiotensin-converting enzyme (ACE) inhibitors, isotretinoin, as well as
omeprazole, etanercept, and BCG vaccine. Drug-induced pityriasis rosea-like
eruption is often slower to resolve than the idiopathic form.
The
eruption has been reported during immunosuppressive treatment with oral
corticosteroids and after bone marrow transplantation, but it is not a common
rash seen in such situations.
Clinical Features
Schematic diagram of the primary plaque (herald patch) and the typical distribution
of secondary plaques along the lines of cleavage on the trunk in a Christmas
tree pattern.
Prodromal symptoms are usually absent. The
first manifestation of the disease is usually the appearance of the herald
patch, because it heralds the onset of the
disease and is seen in over 50% of cases, which is larger and more conspicuous than the
lesions of the later eruption and is usually situated on the thigh or upper
arm, the trunk or the neck; rarely may it be on the face, scalp or the penis.
The herald patch is a sharply defined, red colored round or oval thin plaque, soon covered by fine scale. The size commonly varies, can be as small as 1 cm or
as large as 10 cm and rarely there may be more than one herald patch.
After an interval,
which is usually between 5 and 15 days, but may be as short as a few hours or
as long as 2 months, the secondary eruption begins to appear in crops at 2 to
3-day intervals over a week or 10 days. Less often, new lesions continue to develop
for several weeks. In its classical form the eruption consists of discrete oval
lesions, dull pink in color. The center tends to clear and assumes a wrinkled,
atrophic appearance and a tawny color, with a marginal collarette of scale
attached peripherally, with the free edge of the scale internally. The long
axes of the lesions characteristically follow the lines of cleavage parallel to
the ribs in a Christmas tree pattern on the upper chest and back. When
stretched across the long axis, the scales tend to fold across the lines of
stretch, the so-called “hanging curtain” sign.
The lesions are
usually said to be confined to the trunk, the base of the neck and the proximal
limbs. These sites are certainly most consistently and severely affected but
involvement of the face and scalp is quite common, especially in children.
The
disease is usually asymptomatic, sometimes pruritic with mild flu-like
symptoms.
The skin lesions commonly persists for 3–6 weeks and
then spontaneously resolves; but some clear in 1 or 2 weeks and a few persist for as
long as 3 months or longer. In the latter situation,
the possibility of pityriasis lichenoides chronica arises. There may be temporary hyper- or
hypopigmentation, but usually the lesions vanish without trace.
Second attacks of pityriasis rosea
occur in about 2% of cases after an interval of a few months or many years, and
rarely, a partial or complete relapse of a fading eruption may be seen.
Pityriasis rosea may be atypical in
the appearance or distribution of the lesions or in its course. The herald
patch is absent in about 20% of cases. The ‘secondary’ eruption may be almost
generalized or may be limited to a few lesions, often around the herald patch.
At times the eruption may be maximal on the extremities almost sparing the
trunk. Especially in children, the lesions may be predominantly papular or
urticarial in the early stages, but they are soon surmounted by an
inconspicuous ring of fine scales.
Inverse pityriasis rosea involves the axillae and inguinal areas and sometimes
the face. It is more common in younger children and in those with darkly
pigmented skin.
Diagnosis
In
the typical, fully developed case the diagnosis usually presents little difficulty
as the distribution, morphology and the absence of constitutional symptoms are
sufficiently distinctive.
Differential Diagnosis
Seborrheic dermatitis may be
pityriasiform. There is no herald patch, the lesions often develop slowly and
are most numerous on the upper trunk near the midline, on the neck and in the
scalp, and they are duller in color with thicker and greasier scales. Small,
scaly, follicular papules may also be present. The eruption is persistent if
untreated.
Pityriasis rosea can sometimes be difficult to distinguish
from secondary syphilis. The
genital and oral mucosae should be examined.
The presence of cutaneous signs such as split papules and condyloma lata points
to syphilis, as does the history or presence of a primary chancre. There is no herald
patch and the lesions are roseolar or maculopapular. Patients with secondary syphilis usually have more systemic
complaints, and they often have peripheral lymphadenopathy. Histologically, the
absence of plasma cells favors pityriasis rosea and nowadays
immunohistochemical staining for spirochetal antigens can be done. Serologic
testing – e.g. Venereal Disease Research Laboratory (VDRL), fluorescent
treponemal antibody absorbance (FTA-ABS) – allows the diagnosis of secondary
syphilis to be confirmed.
The
herald patch or generalized eruption can resemble tinea corporis or nummular
dermatitis. The
lesions of ringworm are red and edematous and may show marginal vesiculation.
In case of doubt scrapings from the edge of the lesions should be examined
microscopically for mycelium.
The presence of the collarette of scale, the orientation of
the lesions, and the history can help distinguish pityriasis rosea from
nummular dermatitis, but it can be difficult in the case of vesicular pityriasis
rosea. Guttate
psoriasis and pityriasis lichenoides may sometimes need exclusion. In both, the
lesions are papular and persistent. In psoriasis they are surmounted by silvery
scales. Guttate psoriasis usually has a
thicker scale, smaller size, and lacks the fir-tree distribution. In pityriasis lichenoides they are
polymorphic, some showing hemorrhagic crusting and some adherent scales and should also be considered, especially when lesions last
longer than 4 months.
Treatment
Because pityriasis rosea is often asymptomatic and
self-limited, patient education and reassurance represent a satisfactory
treatment plan. In patients with pruritus, low- to medium-strength topical
corticosteroids may be needed for symptomatic relief. In more severe cases, UVB
phototherapy (broadband or narrowband) or natural sunlight exposure and oral
antihistamines can be used.
Based on the concept of HHV-6 or HHV-7 as a cause of the
eruption, trials of antiviral drugs are reported. High-dose acyclovir (800 mg
five times daily for 1 week) in adults, may lead to a more rapid clearance of
skin lesions. Acyclovir may be effective in the treatment of
PR, especially in patients treated in the first week after the onset of the
eruption, when replicating viral activity of HHV is probably very high. Lower
dosages of 400 mg 5 times a day for 1 week may be equally effective. Institution of acyclovir therapy should not be
withheld even if patients present later than 1 week.
The use of oral
erythromycin antibiotic (1 g four times a day for 2 weeks for adults) is
reported to clear the disease within 2 weeks of treatment but subsequent
studies with erythromycin and azithromycin have not confirmed any effect.
