Shingles (Herpes Zoster) Distribution Pattern
Shingles typically presents as a unilateral rash confined to a single dermatome and does not normally erupt on both sides of the back simultaneously. 1
Typical Presentation of Shingles
Herpes zoster (shingles) is characterized by:
- A unilateral, vesicular eruption with dermatomal pain that often precedes the skin findings by 24-72 hours 2
- Progression from erythematous macules to papules, vesicles, pustules, and finally small ulcers 2
- Distribution limited to a single affected dermatome due to reactivation of the varicella zoster virus that has remained dormant in sensory ganglia 3
The most common sites affected by shingles include:
- Thoracic dermatomes (56%)
- Cranial nerves (13%)
- Lumbar (13%)
- Cervical (11%)
- Sacral nerves (4%) 3
Atypical Presentations
While shingles typically presents unilaterally, there are important exceptions:
- Immunocompromised patients (including those with HIV, cancer, transplant recipients, or on immunosuppressive medications) are at higher risk for atypical presentations including multidermatomal involvement and disseminated disease 1
- Elderly patients and those with underlying malignancies may also experience atypical or multidermatomal presentations 1
- Multiple-site herpes zoster is more difficult to diagnose, requires more aggressive antiviral therapy, carries a higher risk of complications, and may indicate underlying immunosuppression warranting investigation 1
Diagnostic Considerations
When evaluating a patient with bilateral back rash:
- Consider alternative diagnoses if lesions appear simultaneously on both sides of the back
- Diagnosis of shingles is typically made based on clinical presentation and prodromal symptoms 1
- Confirmation can be obtained through direct testing of lesion material:
- PCR testing of vesicle fluid
- Direct fluorescent antibody testing
- Viral culture from blister material 1
Management Implications
The treatment approach differs based on presentation:
- Standard unilateral shingles: Oral antiviral therapy (valacyclovir 1000 mg three times daily, famciclovir 500 mg three times daily, or acyclovir 800 mg five times daily) for 7 days 1
- For immunocompromised patients or those with disseminated/multidermatomal disease: High-dose intravenous acyclovir with transition to oral therapy once clinical improvement occurs 1
- Treatment should continue until all lesions have crusted over 1
Important Caveats
- Bilateral or disseminated shingles may indicate immunosuppression that requires investigation 1
- While the pain and rash of shingles typically present unilaterally, research has shown that sensory neuron damage can occur bilaterally even when the clinical presentation is unilateral 4
- Shingles can occasionally present with atypical symptoms, such as acute abdominal pain, before the characteristic rash appears 5
If a patient presents with bilateral back rash that resembles shingles, consider other diagnoses or potential immunocompromise requiring more aggressive evaluation and management.