18.
A 21-year-old woman presents with the above skin findings on her back. She says the lesions are itchy and have gradually increased in number over the past couple of weeks. She is sexually active and infrequently uses barrier contraception. Her palms and soles show no abnormalities. Which of the following is the most likely diagnosis?
This spot diagnosis is exceedingly HY on the USMLE!
Pityriasis rosea is a self-limiting cutaneous eruption with a very characteristic presentation:
- Begins as a herald patch, or mother patch, which is an erythematous, round to oval, scaly patch or plaque, 2-10 cm in diameter, with a depressed center and raised border.1
- This is followed by crops of smaller lesions that erupt on the trunk and proximal extremities in a “Christmas tree” distribution (i.e., the eruption on the trunk/back + proximal shoulders is apparently euphemized to resemble a Christmas tree).1, 2
- The rash lasts 1-8 weeks in 85% of patients, with an average duration of 5 weeks, before self-resolving.3
- About half of cases are preceded by a non-specific upper respiratory tract-like presentation.4
- The rash is described as mildly to severely pruritic in 25% of patients.4
- Greatest incidence is 20-29 years of age.4
The exact etiology of pityriasis rosea may be manifold, however viral infection with human herpes virus 6 and 7 (HHV6/7), particularly HHV7, is believed to be highly associated.5, 6, 7, 8
- “Although the detection of HHV7 DNA in peripheral blood mononuclear cells (PBMC) and tissues does not prove directly a causal role, HHV7 DNA in cell-free plasma corresponds to active replication which supports a causal relationship. We propose that pityriasis rosea is a clinical presentation of HHV7 reactivation.”5
- “Light and electron microscopy findings suggest infection with human herpesviruses 6 and 7 (HHV6/7). These viral antigens have been detected in skin lesions by immunohistochemistry and their DNA has been isolated from non-lesional skin, peripheral blood mononuclear cells, serum, and saliva samples.”6
- “Pityriasis rosea is an acute exanthem with many clinical and epidemiologic features of an infectious disease. To date, human herpesvirus (HHV)-6 and HHV-7 appear to be the most indicted culprits.”7
- “Nested polymerase chain reaction and in situ hybridization enabled detection of human herpesvirus-7 and human herpesvirus-6 in skin and other tissues isolated from patients with pityriasis rosea. These results suggest that pityriasis rosea is associated with systemic active infection with both human herpesvirus-7 and human herpesvirus-6.”8
Atopic dermatitis is the most common chronic skin disease in children, typically presenting <2 years of age. It is characterized by pruritic eczema flares and often seen as part of the atopy constellation (asthma, allergic rhinoconjunctivitis, eczema). Serum IgE and eosinophils may be elevated.9 Treatment is with emollients and topical steroids.10
Tinea versicolor is a cutaneous fungal infection caused by Malassezia furfur.11 It is described as oval macules that coalesce into larger patches with a fine scale on the shoulders, chest, and back. The yeast blocks melanin synthesis in the skin and also produces a skin bleaching agent. With ultraviolet exposure, a hypopigmented spotted appearance is enhanced due to contrast with the darkened surrounding skin.12 Treatment is typically with topical selenium.13
Nummular eczema is characterized by an itchy rash that forms coin-shaped patches on the skin. It is treated with topical steroids.14
Seborrheic dermatitis is a chronic inflammatory skin disorder often caused by the fungus Pityrosporum ovale. It is characterized by powdery or greasy scales in skin folds and along hair margins. Treatment is usually selenium or ketokonazole shampoo.15
Lichen planus is a skin condition characterized by the 6Ps – purple, pruritic, polygonal, planar, papules, and plaques). It is associated with hepatitis C infection.16
Secondary syphilis notably produces a body rash that includes the palms and soles. Treatment of syphilis is with penicillin.17 This patient’s palms and soles are unaffected.
Bottom line: Pityriasis rosea is a self-limiting cutaneous eruption classically manifesting as a herald patch followed by the emergence of a rash that spreads in a “Christmas tree” distribution. The exact etiology may be manifold, however viral infection with human herpes virus 6 and 7 (HHV6/7), particularly HHV7, is believed to be highly associated. This is an important spot diagnosis on the USMLE. Be familiar with the image.
1) https://www.ncbi.nlm.nih.gov/books/NBK513301/
2) https://www.ncbi.nlm.nih.gov/books/NBK448091/
3) https://www.ncbi.nlm.nih.gov/pubmed/2595391
4) https://www.aafp.org/afp/2004/0101/p87.html
5) https://www.ncbi.nlm.nih.gov/pubmed/9529560
6) https://www.bmj.com/content/351/bmj.h5233
7) https://www.ncbi.nlm.nih.gov/pubmed/20797508
8) https://www.sciencedirect.com/science/article/pii/S0022202X15300324
9) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4470205/
10) https://www.ncbi.nlm.nih.gov/pubmed/18208463
11) https://www.sciencedirect.com/topics/medicine-and-dentistry/tinea-versicolor
12) https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/tinea-versicolor
13) https://www.ncbi.nlm.nih.gov/books/NBK293716/
14) https://www.aocd.org/page/NummularEczema
15) https://www.aafp.org/afp/2000/0501/p2703.html
16) https://www.aafp.org/afp/2011/0701/p53.html
17) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1071050/