PITYRIASIS ROSEA
Pityriasis rosea is a
common idiopathic rash with a characteristic onset and distribution. It is a self-limited
rash that spontaneously resolves within a few months. A few distinct clinical
variants have been described. The main goal in treatment is to differentiate
pityriasis rosea from other rashes that can have a similar clinical picture.
Clinical
Findings: Pityriasis rosea is a common rash of young adults and
children. It has no racial predilection. It is most often seen during the
spring and fall months. Clustering of cases has been reported. A small but
significant subset of patients have had a preceding upper respiratory tract
infection. This has led some to search for a viral cause of the rash, although
none have been found. The rash of pityriasis rosea can have a varying
morphology, but it most commonly begins with a herald patch. The herald patch,
or mother patch, is the first noticeable skin lesion. It typically precedes the
entire outbreak of pityriasis rosea by a few days. The herald patch is a 2- to
4-cm, pink-red patch with fine adherent scale that commonly occurs on the
trunk. After a few days, smaller, oval-shaped patches 0.5 to 1 cm in diameter
begin appearing on the trunk and extremities. The rash follows the skin tension
lines and has a peculiar “fir tree” pattern. This pattern mimics the
down-sloping branches of a fir tree. The rash typically spares the face and
glabrous skin.
Patients may complain of mild to moderate pruritus,
but most are asymptomatic. The main differential diagnosis includes guttate
psoriasis and, in cases that affect the palms and soles, secondary syphilis.
Pityriasis rosea is a self-limited, spontaneously resolving rash. It typically
does not last longer than 2 to 3 months. Guttate psoriasis usually begins after
a streptococcal infection and does not exhibit a herald patch. The teardrop
shaped patches of guttate psoriasis also do not follow the skin tension lines,
and this fact can be used to differentiate the two. Tinea corporis is almost
always in the differential diagnosis of any rash that has a patch type morphology and fine surface scale. Tinea corporis
can be easily diagnosed with a microscopic evaluation of a small scraping of
the skin. Widespread tinea is almost always associated with onychomycosis, and
it is more commonly seen in patients who are taking chronic immunosuppressive
agents or using topical steroids. These traits can be used to help
differentiate the two conditions. The rash of secondary syphilis is the great
mimicker. Any patient who has pityriasis rosea that affects the palms and or
soles should be tested for syphilis.
A few unique variants of pityriasis rosea exist. One
is papular pityriasis rosea. This form more commonly affects school-aged
children with Fitzpatrick type IV, V, or VI skin. This version tends to be a
bit more wide spread and
more pruritic. Instead of small, oval-shaped patches, this variant consists of
small (0.5 cm) papules that have a small amount of surface scale. It runs the
same benign course, with self-resolution after a few weeks to months. On
healing, postinflammatory hyper-pigmentation or hypopigmentation may result and
may persist for several months.
Histology: A superficial
and deep lymphocytic and histiocytic infiltrate is seen surrounding the vessels
of the dermis. Varying
amounts of extravasated red blood cells are appreciated within the upper
dermis. The stratum corneum shows varying degrees of acanthosis and
parakeratosis.
Pathogenesis: Many attempts
to isolate a viral or a bacterial element in patients with pityriasis rosea
have been met with frustration. To date, no infectious cause has been
determined. The true nature and cause of pityriasis rosea remain elusive.
Treatment: No therapy is
needed. Most cases are asymptomatic and mild. Pruritus can be treated with oral
antihistamines and adjunctive topical steroids. The use of oral erythromycin,
twice a day for 2 weeks, was shown to decrease the duration of the rash.
Ultraviolet therapy is very helpful in treating the rash and pruritus. If there
is any consideration for syphilis in the history or the physical examination, a
rapid plasma regain (RPR) blood
test should be performed.
