Is Herpes Zoster Always Unilateral?
Herpes zoster typically presents as a unilateral, dermatomal rash, but it is not always strictly unilateral—disseminated herpes zoster can involve multiple dermatomes bilaterally, particularly in immunocompromised patients. 1
Classic Presentation: Unilateral Dermatomal Distribution
The hallmark presentation of herpes zoster is indeed unilateral:
- The vesicular rash characteristically appears in a unilateral and dermatomal pattern along dorsal root or cranial nerve ganglia. 2, 3, 4
- This unilateral distribution reflects the pathophysiology: VZV reactivates from a single dorsal root ganglion or cranial nerve ganglion where it has remained latent since primary varicella infection. 5, 6
- The rash progresses through stages of clear vesicular clusters, pustulation, ulceration, and crusting, all confined to the affected dermatome(s) on one side of the body. 2
Important Exception: Disseminated Herpes Zoster
Disseminated herpes zoster is defined by skin lesions involving more than three dermatomes, which can cross the midline and appear bilateral. 1
High-Risk Populations for Dissemination
- Immunocompromised patients—including those on active chemotherapy, with HIV infection, receiving chronic immunosuppressive agents, or post-organ transplantation—are at substantially higher risk for disseminated disease. 1
- Patients on B-cell depleting therapies (e.g., ocrelizumab, rituximab, ofatumumab) face the highest risk of severe and disseminated herpes zoster. 1
Clinical Implications of Dissemination
- Disseminated disease may also involve visceral organs (hepatitis, pneumonia, encephalitis) or present with hemorrhagic lesions, requiring escalation to intravenous acyclovir 10 mg/kg every 8 hours. 1
- Immunocompromised patients may develop chronic poorly healing ulcers with persistent viral replication, further complicating the clinical picture. 7
Common Pitfalls to Avoid
- Do not assume bilateral or multi-dermatomal lesions exclude herpes zoster—this presentation mandates urgent evaluation for disseminated disease and potential visceral involvement. 1
- In immunocompromised hosts, loss of the typical vesicular component can occur, with lesions appearing as chronic ulcers from onset, making diagnosis more challenging. 7
- Clinicians may underestimate the severity when atypical presentations lack characteristic vesicular appearance, delaying appropriate intravenous therapy. 7
Transmission Considerations
- Patients with disseminated zoster require both airborne and contact precautions in healthcare settings, not just contact precautions as with localized disease. 1
- All patients with active herpes zoster should avoid contact with susceptible individuals until all lesions have crusted, as the virus can be transmitted through direct contact or aerosolized vesicular fluid. 5, 1