Pityriasis rosea

Clinical case scenario

Emma Jenkins is 21 years old and reaching 24 weeks gestation in her first pregnancy. She attended the surgery a week ago having noticed a slightly itchy erythematous patch on her chest. She also had vaginal thrush symptoms and was treated with an anti-fungal pessary and given topical clotrimazole for the likely tinea patch. She attends today complaining of a widespread rash all over her torso which is uncomfortable and itchy. When you examine her there is a symmetrical rash over her torso and the typical Christmas tree distribution of pityriasis rosea. Her concerns include anxiety about possible harm to her baby and the uncomfortable pruritus. She asks if the treatment given for ringworm was incorrect.

Aetiology

Pityriasis rosea does not have a definite aetiology. Possible causes have been suggested, but none are confirmed. It has been linked with viral infections, as almost 70% of patients have a prodromal illness with sore throat, fever or gastrointestinal disturbance before the appearance of the herald patch (Drago et al., 2016). Reactivation of latent human herpes virus-6 and 7 has been implicated as a possible aetiological factor (Mahajan et al., 2016). Possible links have also been made, but not confirmed, between pityriasis rosea and some vaccinations such as bacille Calmette-Guerin (BCG), influenza, pneumococcus and more recently to the covid-19 vaccine (Khan, 2023; Litchman et al., 2022).

Presentation and diagnosis

Pityriasis rosea is a benign rash and often occurs between the ages of 10 and 35 years. The disease course usually starts with the herald patch, seen in over half of cases. The patch is typically between 2 and 5 cm in diameter and is erythematous, often with an elevated scaling border (Fig. 1).

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Figure 1.

Herald patch of pityriasis rosea.

The herald patch can often be misdiagnosed as eczema or ringworm. Within 2 weeks, generalised pinkish scaly oval plaques form and are distributed symmetrically over the thorax, back, abdomen and sometimes the limbs. The lesions often have a collarette appearance to them, with the edges peripherally attached and lifted up near to the centre of the lesion. In pityriasis rosea, the scale does not extend to the border of the lesion as it does in tinea corporis. The plaques often follow the Langer's lines of cleavage forming a typical ‘fir tree’ or ‘Christmas tree’ distribution on the back (Fig. 2).

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Figure 2.

Christmas tree distribution of pityriasis rosea following Langer’s lines of cleavage.

Moderate-to-severe pruritus can affect up to half of patients with pityriasis rosea (Villalon-Gomez, 2018). The rash lasts 6 to 8 weeks on average, but can be prolonged for up to 3 months (Drago et al., 2016). Hypopigmentation and hyperpigmentation of the skin can follow resolution of the rash. In darker skin, the herald patch tends to be a dark violet to deep brown colour and the following smaller lesions are more purple-to-brown in tone and appear as raised bumps on the skin (Fig. 3). Hyperpigmentation often follows, usually resolving within 6 to 12 months and is the most common morbidity from pityriasis rosea in patients with darker skin (Lawrence, 2022).

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Figure 3.

Purple/brown coloured lesions are more likely in patients with darker skin.

Pityriasis rosea is not considered to be contagious, and patients are not advised to isolate to avoid transmission. There have been a few reports of family members developing symptoms simultaneously. However, there is no clear evidence of an infectious cause for pityriasis rosea (Ashayer et al., 2018).

Atypical presentations

The classic presentation of pityriasis rosea makes diagnosis easy once the smaller lesions erupt. Atypical presentations, however, can present a diagnostic challenge and occur in approximately a fifth of cases. Atypical presentations include variety in morphology, distribution and natural courses. Some examples include:

Inverse distribution: The lesions are distributed on the extremities and flexural areas including axillae, groins, palms, soles, neck and face, sparing the trunk (Ermetcan et al., 2010)

Other atypical presentations include an absent herald patch, a solitary herald patch without generalised eruptions or a herald patch being present in an atypical area, such as the sole of the foot. Variations in the morphology of the rash include urticarial pityriasis rosea, purpuric pityriasis rosea, follicular pityriasis rosea and vesicular pityriasis rosea.

Atypical presentations can be referred to Dermatology for help in diagnosis, with for example, dermoscopic evaluation using a triple-light source and skin biopsy. A biopsy confirming pityriasis rosea will show focal paraketosis, with or without acanthosis, spongiosis (perivascular infiltrate of lymphocytes and histiocytes) and sometimes extravasation of red cells. Biopsies are characteristic, but not pathognomonic. Where tinea is suspected as an alternative diagnosis, potassium hydroxide examination of scales for dermatophyte hyphae may be useful to establish the cause of the rash (Hsu et al., 2001).

Differential diagnoses

A number of differential diagnoses should be considered in patients with a pityriasis rosea-like rash. These include guttate psoriasis, secondary syphilis, seborrheic dermatitis, nummular eczema, tinea corporis, lichen planus and pityriasis lichenoides chronic. Distinguishing features are highlighted in Table 1.

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Table 1.

Differential diagnoses

Differential diagnoses	Distinguishing features
Guttate psoriasis	Absence of herald patch, histopathology distinguishes the features with more uniform distribution and diffuse white scales in guttate psoriasis whereas pityriasis rosea has more non-specific distribution and scales are more brown or white pigmented
Secondary syphilis	Lymphadenopathy often present and palmar, plantar and mucous membrane lesions. Lesions are more brown/red with oval macule and papules. Syphilis serology is confirmative
Seborrheic dermatitis	Scalp involvement in seborrheic dermatitis with flaking skin and more patches of greasy skin covered in white or yellow scales, more prevalent in winter
Nummular eczema	More intense pruritus in nummular eczema; lesions are larger around 4 cm and coin-shaped
Tinea corporis	Scales in pityriasis rosea do not extend to the border of the lesion as in tinea corporis.
Lichen planus	Purple, scaly plaques and papules on the body, often crossed with fine white lines. Distribution mostly on wrists, lower back and ankles. Mucosal and genital involvement with patches on vulva or penis often present.
Pityriasis lichenoides chronic	Widespread red-brown papules with central scales and a more random distribution on trunk.

A pityriasis rosea-like rash can also be caused by some drugs, including ACE inhibitors, hydrochlorothiazide, barbiturates, gold, metronidazole and allopurinol (Villalon-Gomez, 2018). This rash will usually resolve on withdrawal of the medication, confirming the drug as the causative agent. Other features distinguishing a drug-induced pityriasis rosea-like rash from classic pityriasis rosea include the lack of the herald patch, absence of prodromal symptoms, brighter inflammatory lesions, more intense pruritus with reduced benefit from anti-histamines and increased eosinophils in the blood and skin infiltrate in histopathologic analysis (Lahouel et al., 2021; Panda et al., 2014).

Pityriasis rosea and pregnancy

There is an increased risk of developing pityriasis rosea in pregnancy, likely due to an altered immune response (Drago et al., 2016). Studies assessing outcomes of pregnancy in patients with pityriasis rosea are limited, so a significant link between pityriasis rosea and unfavourable pregnancy outcomes has not been established. There have, however, been some reports of miscarriage, preterm delivery, low birth weight and weak motility or hypotonia in the neonate, especially if the mother is affected before 15 weeks gestation (Drago et al., 2008). Patients with pityriasis rosea before 15 weeks gestation or with atypical presentations will, therefore, benefit from close monitoring in their antenatal care and from dermatology input. In primary care, advice should be sought from secondary antenatal care services in any patient presenting with pityriasis rosea in pregnancy, regardless of the gestation, to assess how closely the patient will require monitoring (Wenger-Oehn et al., 2022).

Treatment

Pityriasis rosea is mostly a self-limiting condition and usually resolves spontaneously within 12 weeks. The mainstay of management, therefore, remains watchful waiting and reassurance. Treatment options, if required, are for symptomatic relief. In secondary care, treatment may be offered to promote resolution when symptoms are atypical, more severe or prolonged beyond 12 weeks. At the point of initial presentation with just a herald patch definite diagnosis can be difficult, as highlighted in the case scenario. At this stage, it is reasonable to consider other common causes of the symptoms, such as tinea corporis, but bear alternative differential diagnoses in mind. The basic principle of conducting a clear and focussed history and examination helps correct diagnosis. For example, a history of a prodromal illness prior to appearance of the herald patch makes a diagnosis of pityriasis rosea more likely.

Since any treatment of pityriasis rosea is purely symptomatic at this stage it is reasonable to adopt a wait and watch approach, the case particularly if the patient is not experiencing any symptoms of pruritus or discomfort. The patient can be reassured at this stage with a planned follow up after a week for review.

Once the secondary eruptions appear, symptomatic relief can be offered with emollients, oral anti-histamines and medium potency topical steroid creams. Emollients help to soothe the skin and reduce skin dryness, when appropriate. Oral anti-histamines will reduce pruritus. Steroid creams are added if the pruritus does not settle with anti-histamines alone and to reduce any swelling and inflammation if necessary. In children the benefit of prescribing steroid creams should be weighed against the risks and reserved for moderate-to-severe symptoms if there is little relief from anti-histamines alone. Patients can be advised to avoid soaps and shower gels in order to avoid drying the skin and use a soap substitute instead. If the pruritus is more severe, then zinc oxide and calamine lotion are recommended, either separately or in combination. Oral steroids can be considered, but are reserved for extensive rash and very symptomatic cases usually after consultation with a dermatologist (Sonthalia et al., 2018).

Potential treatment options

Key points

Pityriasis rosea typically causes a mild, self-limiting rash lasting 6 to 8 weeks, with an initial herald patch