Pityriasis Rosea

Pityriasis rosea, also known as pityriasis rosea Gibert, is a type of skin rash that typically begins with a single red and slightly scaly area known as a "herald patch". This initial lesion is followed by an eruption of many smaller, scaly spots. The rash is pinkish with a red edge in lighter skin tones, and greyish in darker skin tones. The condition generally resolves within three months without treatment. It most commonly affects individuals between the ages of 10 and 35.

Signs and Symptoms

The onset of pityriasis rosea may follow recent upper respiratory tract infections, as reported by some studies in 8–69% of patients. Occasionally, prodromal flu-like symptoms such as headache, joint pain, mild fever, fatigue, nausea, diarrhoea, or vomiting may precede the rash. Typically, the first sign is a single, 2 to 10 cm oval red "herald" patch, often mistaken for ringworm. This patch usually appears on the trunk or neck and may be hidden in areas like the armpit.

Days or weeks after the appearance of the herald patch, a rash of smaller pink or red, flaky spots appears, primarily on the trunk and upper limbs, following the skin's cleavage lines. This distribution often results in a characteristic "christmas-tree" pattern. In 6% of cases, an "inverse" distribution occurs, with the rash predominantly on the extremities. About one in four individuals experience mild to severe itching, which worsens with scratching.

Approximately 20% of cases are atypical, presenting variations in the size, distribution, and morphology of the lesions. Some forms may mimic other conditions such as chicken pox or erythema multiforme.

Causes

The exact cause of pityriasis rosea is unclear, but it is believed to be related to viral infections, particularly human herpesvirus 6 (HHV6) or human herpesvirus 7 (HHV7). However, not all studies support this association. Certain medications can also result in a similar rash.

Diagnosis

Diagnosis is mainly clinical, based on the characteristic symptoms. Misdiagnosis is not uncommon, especially among non-dermatologists. Tests to rule out other conditions, such as Lyme disease, ringworm, psoriasis, eczema, drug eruptions, and viral exanthems, may be necessary. Secondary syphilis should be excluded with rapid plasma reagin testing if clinically indicated.

A set of validated diagnostic criteria for pityriasis rosea includes essential, optional, and exclusional clinical features. Essential features include discrete circular or oval lesions with peripheral collarette scaling. Optional features include a herald patch and truncal distribution of lesions. Exclusional features include vesicles at the centre of lesions and lesions on palmar or plantar surfaces.

Treatment

Pityriasis rosea usually resolves on its own, and treatment is not required. Oral antihistamines or topical steroids may alleviate itching, though steroids can prolong the time it takes for new skin to match the surrounding skin colour. Avoiding irritants such as fragrant soaps, chlorinated water, and synthetic fabrics can help. Lotions that prevent or reduce itching may also be beneficial.

Exposure to direct sunlight can hasten lesion resolution. Ultraviolet (UV) therapy has been used to speed up recovery, but its efficacy in reducing itching is debated.

A 2007 meta-analysis found insufficient evidence to support the effectiveness of most treatments. While early studies suggested oral erythromycin might be effective, subsequent research did not confirm these results. Notably, some patients reported that their pityriasis rosea resolved after receiving the monkeypox vaccine, with no recurrence observed in follow-up studies.

Prognosis

In most cases, pityriasis rosea lasts a few weeks to six months and resolves completely without long-term effects. Recurrence is rare, occurring in less than two percent of cases.

Epidemiology

The prevalence of pityriasis rosea in the United States is approximately 0.13% in men and 0.14% in women, with higher incidence during spring. The condition is not considered contagious, although small outbreaks have been reported in communal settings like fraternity houses, military bases, and schools.

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Self-assessment MCQs (single best answer)

What is the initial lesion of pityriasis rosea commonly called?

In what age group is pityriasis rosea most commonly seen?

Which of the following is NOT a common symptom that may precede the rash in pityriasis rosea?

What pattern is commonly associated with the distribution of pityriasis rosea lesions?

Which viral infections are believed to be related to the cause of pityriasis rosea?

What is the primary method for diagnosing pityriasis rosea?

Which treatment is commonly used to relieve itching in pityriasis rosea?

What should be avoided to help manage pityriasis rosea?

How long does pityriasis rosea typically last?

What is the recurrence rate of pityriasis rosea?