Human Herpesvirus 7 – HHV7
Human herpesvirus 7 (HHV-7) is a double-stranded DNA virus in the subfamily Betaherpesvirinae, genus Roseolovirus, and is a close genetic relative of HHV-6. Whereas HHV-6B enters cells via the CD134 receptor, HHV-7 uses the CD4 molecule on the surface of T-helper cells as its main entry receptor, competing directly with the binding site used by the gp120 protein of HIV-1.
HHV-7 is mainly passed on through saliva during childhood. After the primary infection (which usually causes a mild, nonspecific fever or a roseola-type rash), the virus remains latent for life in CD4+ T cells and the salivary glands. Reactivation of HHV-7, alone or together with HHV-6, is considered the most likely microbial trigger of pityriasis rosea (Gibert).
Pathogenesis and the Link With Pityriasis Rosea
CD4 Receptor Affinity and Biological Competition
- Entry receptor: The virus binds directly to the D1 domain of CD4, leading to down-regulation of CD4 on the surface of infected T-helper cells.
- Interaction with HHV-6: Reactivation of HHV-7 in T cells may act as a transactivator, setting off reactivation of latent HHV-6 and producing a dual immune response in the skin.
How Pityriasis Rosea Is Triggered
- Reactivation of HHV-7/HHV-6 in the skin sets off a T-cell-mediated delayed hypersensitivity reaction.
- CD4+ T cells and Langerhans cells cluster densely around small vessels in the upper dermis and release proinflammatory cytokines. These cause vasodilation, mild exocytosis and spongiosis of the epidermis, producing the characteristic collarette of scale.
Clinical Features of Pityriasis Rosea
The Initial Lesion (Herald Patch):
- Appears first in 80% of cases, usually on the trunk, neck or upper limbs.
- Appearance: a large (2–10 cm), well-defined, oval pink or salmon-pink patch.
- Collarette scale: the center of the patch is slightly paler with fine scaling, and a thin rim of scale is attached at the outer edge with its free margin pointing toward the center.
The Secondary Eruption: "Christmas-Tree" Pattern
- Some 7–14 days after the herald patch, a widespread crop of smaller lesions appears.
- Appearance: Numerous smaller (0.5–2 cm) oval, salmon-pink macules and papules, also with a collarette of scale.
- "Christmas-tree" distribution: The long axes of the oval lesions line up along the skin cleavage lines (Langer's lines) on the back and chest, resembling the drooping branches of a fir tree.
- Symptoms: About 50% of patients have mild to moderate itch, which worsens after hot showers or sweating. The rash clears on its own within 4–8 weeks.
Standard Diagnostic Workup at Haute-Derma
Clinical Examination and Dermoscopy:
- Look for the herald patch and for lesions aligned along Langer's lines.
- Dermoscopy:
- Pale yellow to orange-pink background.
- A fine white rim of scale peeling at the inner edge (collarette sign).
- Scattered dotted vessels, not arranged along a raised border.
Mandatory Tests to Exclude Other Conditions:
- KOH microscopy: Scale from the edge of a lesion is examined to rule out tinea corporis.
- Syphilis serology (RPR/VDRL): Required for every patient with a widespread scaly rash, to rule out secondary syphilis, a serious mimic of pityriasis rosea.
Management and Treatment at Haute-Derma
Topical and Systemic Treatment
- Soothing irritation and itch:
- Bathe in cool or lukewarm water with a gentle, soap-free wash.
- Apply a ceramide or colloidal oatmeal moisturizer 2–3 times a day.
- A second-generation H1 antihistamine (levocetirizine 5 mg or desloratadine 5 mg daily).
- Topical corticosteroids: Hydrocortisone butyrate 0.1% or betamethasone valerate 0.1% once daily for 7–10 days on very itchy patches.
Narrowband UVB (NB-UVB) Phototherapy
- Indications: Extensive pityriasis rosea with significant itch that does not respond to topical treatment, or disease lasting more than 6 weeks.
- How it works: NB-UVB (311 nm) suppresses T-cell and Langerhans cell infiltration in the dermis, helping the rash fade 2–3 times faster than it would naturally.
- Course: 2–3 sessions a week, starting at 70% of the minimal erythema dose (MED) and increasing by 10% each session.
