A herald is a sign that something is soon going to happen and the herald patch (mother patch) of pityriasis rosea is a solitary larger and more conspicuous patch that precedes other patches. The herald patch and the succeeding patches are similar histopathologically (mild psoriasiform hyperplasia; spongiosis and exocytosis of lymphocytes leading to ‘mini-Pautrier simulants’ simulating Pautrier microabscesses because of the aggregation of lymphocytes; focal parakeratosis). The interval is usually a week or so, but may be as short as a few hours or as long as 2 months. This is a characteristic evolutionary sequence seen in this skin condition that is believed to be due to reactivation of HHV-6 and/or HHV-7. The incidence is highest between the ages of 15 and 40, and the disease is most prevalent in the spring and autumn/winter. Females are more frequently affected than males. The herald patch is absent or undetected in about 20% of cases. Rarely, there may be more than one herald patch. The mother patch may be the sole manifestation of the disease! The reported epidemiological evidence for infectivity of pityriasis rosea includes occasional family or household outbreaks, seasonal and year-to-year fluctuations and statistical evidence for clustering in space and time. Interestingly, clusters of cases of herpes zoster have also been reported, and it is suggested that exposure to exogenous varicella zoster virus may trigger reactivation of latent virus in such circumstances.
The herald patch is a sharply defined oval or round salmon-red patch or slightly raised plaque with a marginal collarette of scale attached inside the periphery, with the free edge of the scale internally. Actually, the word collarette is used because the scale is attached inside the periphery and loose towards the centre of the lesion. The herald patch rapidly reaches its maximum size, usually 2–5 cm in diameter but occasionally much larger. The scales are silvery grey. The centre tends to clear and assumes a tawny colour. When stretched across the long axis, the scale tends to fold across the line of stretch, the “hanging curtain” sign. The herald patch is usually on the thigh or upper arm, the trunk, suprapubic skin, the groin or the neck; rarely may it be on the face, scalp or the penis.
The succeeding patches (resembling the mother patch or being non-scaly) begin to appear in crops at 2 to 3-day intervals over a week or so. Less often, new lesions continue to develop for several weeks. The long axes of the lesions characteristically are parallel to the ribs on the upper chest and back. There may be slight or moderate itching. The eruption is usually generalized, affecting chiefly the trunk and sparing sun-exposed surfaces but involvement of the face and scalp is quite common, especially in children. Palms and soles are rarely involved. The eruption may be limited to a few lesions, often around the herald patch. At times, the eruption is confined to a single region, or may be maximal on the extremities almost sparing the trunk. An inverse distribution, sparing covered areas, is not rare. Unilateral pityriasis rosea has been reported. When irritated lesions my develop vesicles simulating erythema multiforme (pityriasis rosea irritata).
Although pityriasis rosea is twice as common in black individuals as white, the same seasonal peaks and preceding herald patch occur. However, in black skin, individual lesions are smaller and more papular (micropapular) often urticated and may even be vesicular. An inverse distribution of pityriasis rosea is more frequent in black skin and involvement of the face is seen in 30%, especially in children. The scalp is also more often affected. Lesions in black patients tend to be quite itchy and are more persistent.
Chuh has drawn up a list of diagnostic criteria for pityriasis rosea. Essential features for the diagnosis include: (i) discrete circular or oval lesions; (ii) scaling on most lesions; and (iii) collarette scaling with central clearance of at least two lesions. Optional clinical features of which one must also be present include: (i) truncal and proximal limb distribution, with less than 10% of lesions distal to the mid-upper arm and mid thigh; (ii) distribution of most lesions along the ribs; and (iii) a herald patch appearing at least 2 days before the generalized eruption. Histopathological features were not added to the criteria, being relatively non-specific. However, Weedon states that histopathological features are sufficiently characteristic to allow the diagnosis to be made. Moreover, histopathological evaluation can be especially helpful in excluding the conditions with which pityriasis rosea may be confused.
Without treatment, the disease duration usually varies between 4 and 10 weeks. A few persist for as long as 3 months. A longer duration, except in localized forms, is very unusual. There may be temporary hyper- or hypopigmentation, but usually the lesions vanish without trace. Postinflammatory hyperpigmentation occurs in almost half of black patients, but hypopigmentation may also occur. Rarely, a partial or complete relapse of a fading pityriasis rosea may be seen. Second attacks occur in about 2% of cases. Pityriasis rosea during pregnancy is of concern (miscarriages and premature deliveries have been reported).
Pityriasis rosea may be atypical in the appearance or distribution of the lesions or in its course. Examples include erythema multiforme-like variants, classic lesions admixed with follicular papules or purpura, and papular pityriasis rosea (absent herald patch). Thus the diagnosis can be challenging. In the typical, fully developed case, the diagnosis is usually straightforward, as the distribution, morphology and the usual absence of constitutional symptoms are sufficiently distinctive. In pityriasis circinata et marginata of Vidal, sometimes regarded as a special form of pityriasis rosea and seen mainly in adults, the lesions are few and large, and are often localized to one region of the body, especially the axillae or groins. They tend to become confluent and may persist for several months. This form may follow a typical generalized pityriasis rosea, but it usually occurs alone. Pityriasis rosea might mimic other viral exanthema. Ackerman used to propose that pityriasis rosea and erythema annulare centrifugum are clinical variations of a single pathological process, and that pityriasis rosea gigantea is pityriasis rosea concurrent with erythema annulare centrifugum.
Seborrhoeic dermatitis may be pityriasiform (pityriasiform type of seborrhoeic dermatitis). There is no herald patch. The lesions often develop slowly and the are more widely distributed; being most numerous on the upper trunk near the midline, on the neck and in the scalp, and they are duller in colour with thicker and greasier scales. Small, scaly, follicular papules may also be present. The eruption is persistent if untreated.
The usual absence of lymphadenopathy, and infrequent mucous membrane lesions help to distinguish pityriasis rosea from secondary syphilis (useful points: remains of a chancre might be seen/history of chancre - no herald patch - roseolar or maculopapular lesions assume a brownish tint with palmoplantar involvement - condylomata lata - mucous membrane lesions – lymphadenopathy - presence of plasma cells on histopathology - positive nontreponemal and treponemal tests).
Some patterns of drug eruption may have to be excluded. An acute onset without a herald patch, itching and a tendency for the lesions to become lichenoid in appearance are suggestive features. A progressive, irritable, atypical pityriasiform eruption in a patient taking a drug, which is known to provoke reactions of this nature, can be provisionally accepted.
Guttate psoriasis and pityriasis lichenoides may sometimes need exclusion. In both, the lesions are papular and persistent. In psoriasis they are surmounted by thicker silvery scales. In pityriasis lichenoides they are polymorphic, some showing haemorrhagic crusting and some adherent thicker scales.
The hypopigmented patches with dry, branny scales of pityriasis alba are most frequent on the face, and are seen mainly in young children. Discoid dermatitis has no collarette of scale and is usually not oval. Tiny vesicles are common.
The acute urticarial forms in childhood can sometimes not be identified with complete certainty on first examination unless a herald patch can be discovered. Re-examination after 2 days enables a confident diagnosis to be confirmed.
The herald patch and the localized forms such as pityriasis circinata et marginata of Vidal can be easily confused with ringworm. The lesions of ringworm are red and oedematous, may show marginal vesiculation and are usually not oval. Scale is usually at the periphery of plaques rather than inside the periphery. The pigmented form of pityriasis versicolor does not show marginal scaling. In case of doubt microscopic examination of scales is performed to differentiate these two conditions.
Scabies and lichen planus may be confused with the papular type of pityriasis rosea.
If itch is troublesome, or the appearance distressing, a topical steroid, usually of moderate strength can be helpful. The standard dose regimen of aciclovir is ineffective, but high-dose acyclovir (herpes zoster treatment dosage), used early after the onset of the eruption, may lead to a more rapid clearance of skin lesions. It has been stated in Fitzpatrick’s Dermatology in General Medicine textbook that this form of therapy should be considered in pityriasis rosea patients presenting early in their disease course who demonstrate associated flu-like symptoms and/or extensive rash.
The centre tends to clear and assumes a tawny (brownish-yellow) colour, with a marginal collarette of scale attached inside the periphery, with the free edge of the scale loose internally.
This page was last updated in February 2016.