A herald patch is an erythematous, 2 to 10 centimeter, round to oval scaly patch or plaque with a depressed center and raised border. It is a common presenting sign in pityriasis rosea. It is called the herald patch because it is frequently present a few days to 2 weeks before the full eruption of pityriasis rosea, a common, self-limiting papulosquamous disorder, appears.
The herald patch and pityriasis rosea are thought to be caused by infection with human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7), but this is still a topic of debate. Evidence supporting an infectious etiology include outbreaks occurring in clusters, the prodromal symptoms that occur in most patients before the herald patch or eruption of pityriasis rosea occurs, and the rare instance of recurrence which suggests immunity. In one retrospective cohort study, pityriasis rosea only recurred in 3.7% of patients, but none of these recurrences manifested with a herald patch. Interactions between Langerhans cells, unknown components of the epidermis, and dermal dendritic cells have also been postulated, but whether these interactions are due to a viral etiology is still uncertain.
The herald patch is seen in approximately 80% of the cases of pityriasis rosea. There is no gender or racial bias. The incidence of pityriasis rosea peaks between the ages of 20 and 29, but it may be seen in any age group.
The pathophysiology of pityriasis rosea, and thus the herald patch, is poorly understood. As stated, there has been an association with HHV-6 and HHV-7 in the plasma and lesional skin of patients with pityriasis rosea, but other studies have revealed conflicting evidence. The inflammatory populations seen in lesions of pityriasis rosea and the herald patch are predominantly T cells with a lack of B cells and natural killer cells. Natural killer cells are cytotoxic to cells infected with viruses, and their presence would be suspected if it was solely due to a viral etiology. Interactions between the Langerhans cells and unknown components of the epidermis have been implicated in the pathophysiology, but this also is not understood.
The immunohistochemical and histopathological findings in the herald patch and fully developed lesions of pityriasis rosea are very similar. Histological findings include focal or confluent parakeratosis, epidermal hyperplasia and spongiosis, exocytosis of lymphocytes, and extravasation of erythrocytes along with a moderately dense perivascular lymphocytic infiltrate in the superficial dermis. Immunohistochemical analysis usually reveals an increased CD4+ to a CD8+ ratio of T lymphocytes and increased numbers of Langerhans cells also have been observed in specimens.
The herald patch is a round to oval erythematous patch or plaque with central clearing and peripheral scale trailing behind the margins of the erythema. The herald patch typically measures 2 to 10 cm. However, rare reports of very large herald patches have been described, with one case nearly covering the entire trunk of an 18-month-old female child. Most herald patches appear on the trunk, neck, or proximal extremities, although in rare cases they have appeared on the face, genitalia, scalp, and acral surfaces. Most lesions are asymptomatic but some may be pruritic. A few days to 2 weeks after the appearance of the herald patch, patients develop the more diffuse eruption of pityriasis rosea. It is accompanied by smaller lesions resembling the herald patch following the Langer lines in a “Christmas tree” pattern, with truncal predominance. Most patients experience prodromal symptoms including a headache, fever, arthralgias, and malaise either before or around the time the herald patch appears.
A definitive diagnosis of the herald patch can be difficult before the classic eruption of pityriasis rosea. Due to morphological similarities it shares with tinea corporis, a potassium hydroxide prep should be performed to rule this out as it is a simple and effective diagnostic test. If the potassium hydroxide prep is equivocal, a biopsy may be performed which may aid in differentiating the herald patch from tinea, erythema annulare centrifugum, or nummular eczema. When the full eruption of pityriasis rosea finally presents, the palms and soles should be checked for involvement as the eruption can mimic secondary syphilis. If secondary syphilis cannot be ruled out, nontreponemal tests such as the rapid plasma reagin test should be performed with appropriate confirmatory tests if needed.
Because the herald patch is a feature of pityriasis rosea, the same treatment is advised for both. The eruption of pityriasis rosea is a benign, self-limited papulosquamous process. No treatment is necessary, and the eruption of both the herald patch and pityriasis rosea should resolve within 8 weeks. Reports of a variant of pityriasis rosea known as persistent pityriasis rosea have been described, with some lasting longer than 12 weeks. The herald patch is seen in most cases, and a higher association with systemic symptoms, oral lesions, and increased HHV-6 and HHV-7 viral loads also were found in association with this form. There have been numerous reports of adverse outcomes in the newborns of pregnant women who developed pityriasis rosea during pregnancy. In an article reviewing the literature, most adverse events occurred when the mothers developed pityriasis rosea in the second trimester, followed by the first trimester. Reported adverse events include prematurity, stillbirth, low gestational weight, and hypotonia.
Patients typically seek treatment for the pruritis that occasionally is associated with pityriasis rosea, or because they are disturbed by the appearance of the rash. Most cases of pityriasis rosea are asymptomatic or minimally pruritic, but approximately 25% of patients experience severe pruritis. For these patients, topical steroids, calamine lotion, zinc oxide, oral antihistamines, and oral steroids may be used. If the patient is disturbed by the appearance of the rash and desires treatment, ultraviolet B phototherapy or a 2-week course of oral erythromycin may be used. Both have been shown to shorten the duration of the eruption.
The differential diagnosis of the herald patch is different than the differential diagnosis of pityriasis rosea because the former is a single lesion while the latter is an eruption. The differential diagnosis for the herald patch includes tinea corporis, nummular eczema, and erythema annulare centrifugum. A helpful distinguishing feature among most of these conditions is the location of the scale within the erythema. The herald patch and erythema annulare centrifugum often exhibit a trailing scale. This is seen as a collarette of scale inside the borders of the erythema. The edge of the scale in tinea often appears to lead the erythema in an annular fashion. Nummular eczema typically has scale throughout the lesion without central clearing.