Harrison's Practice: Shingles and Postherpetic Neuralgia

Harrison's Practice

Shingles and Postherpetic Neuralgia

Symptoms & Signs

Zoster
- Onset of disease is often heralded by pain within the dermatome that may precede eruption of the rash by 2–3 days.
- Prodrome can also include fever, malaise, and headache.
- General characteristics of the rash
  - Most commonly involves a single, unilateral nerve root
  - Erythematous maculopapular rash evolves rapidly into vesicular lesions.
  - Lesions may remain few in number.
  - New lesions may continue to form for 3–5 days.
  - Rash is typically very pruritic and painful.
  - Usually lasts 7–10 days, though skin may not heal completely for 2–4 weeks
- 3 clinical presentations
  - Unilateral vesicular eruption within a dermatome (most frequently between T3 and L3)
  - Zoster ophthalmicus (involvement of ophthalmic branch [V1] of the trigeminal nerve)
    - Pain and rash in the distribution of V1
    - Involvement of the eye is an ophthalmologic emergency.
    - Can lead to blindness if untreated
  - Ramsay Hunt syndrome (involvement of the facial nerve [cranial nerve VII])
    - Pain and vesicles appear in external auditory canal.
    - Ipsilateral facial palsy (upper and lower half of the face, resembling Bell’s palsy)
    - Loss of taste in the ipsilateral anterior two-thirds of the tongue
- Immunocompromised host
  - Similar clinical presentations, though, can be more prolonged and more severe.
  - In immunocompromised patients who develop disseminated cutaneous zoster, there is the risk of involvement of the lungs (pneumonitis), central nervous system (meningoencephalitis), liver, and other organs.
    - Rarely fatal
Postherpetic neuralgia
- Persistent pain and paresthesias in the dermatomal distribution of previous zoster rash
  - May be sharp, stabbing, burning, or aching
  - Can have either hypoesthesia or hyperesthesia on examination
  - Extreme sensitivity to touch and temperature changes

Differential Diagnosis

Zoster
- Coxsackievirus infections
  - Can also produce a dermatomal vesicular rash
- Herpes simplex virus infections
- Contact dermatitis, for instance poison oak or poison ivy
- Prodromal pain can sometimes be confused with angina, appendicitis, duodenal ulcer, or colic (biliary or renal).
Postherpetic neuralgia
- Trigeminal neuralgia
- Mononeuritis
- Traumatic peripheral nerve lesions
- Atypical facial pain

Diagnostic Approach

Zoster
- Diagnosis is almost always made by clinical assessment alone without additional laboratory confirmation.
- Unilateral vesicular lesions in a dermatomal pattern should suggest diagnosis.
- In prodromal stage, diagnosis can be difficult and may be made only after lesions have appeared or by retrospective serologic assessment.
- Occurrence of zoster without a rash can occur (zoster sine herpete).
- Unequivocal confirmation is possible only through 1 of the following:
  - Isolation of VZV in susceptible tissue-culture cell lines
  - Demonstration of either seroconversion or a > 4-fold rise in antibody titer between convalescent- and acute-phase serum specimens
  - Detection of VZV DNA by polymerase chain reaction (PCR)

Postherpetic neuralgia
- Clinical diagnosis: pain syndrome in zoster-affected dermatome following vesicular rash consistent with zoster infection

Laboratory Tests

Zoster
- Serology
  - Unequivocal confirmation of VZV infection if > 4-fold rise in antibody titer between convalescent- and acute-phase serum specimens
  - Most frequently employed serologic tools for assessing host response are:
    - Immunofluorescent detection of antibodies to VZV membrane antigens
    - Fluorescent antibody to membrane antigen (FAMA) test
    - Immune adherence hemagglutination
    - Enzyme-linked immunosorbent assay (ELISA)
  - FAMA test and ELISA appear to be the most sensitive.
- PCR
  - PCR technology for detection of viral DNA in vesicular fluid
    - Available in a limited number of diagnostic laboratories
- Tissue cultures
  - Isolation of VZV in susceptible tissue-culture cell lines gives unequivocal confirmation of diagnosis.
Postherpetic neuralgia
- No laboratory tests are indicated.

Imaging

Routine imaging is not indicated.

Diagnostic Procedures

Zoster
- Tzanck smear
  - Tzanck smear of scraping from base of lesions to demonstrate multinucleated giant cells is rapid but has low sensitivity (~60%).
- Cerebrospinal fluid analysis usually is not indicated unless central nervous system involvement is suspected.
  - Asymptomatic meningitis may be present.
    - Pleocytosis
    - Moderately elevated protein levels

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