Laboratory Studies
Diagnosis of herpetic whitlow usually is clinical, based on presentation of the affected digit with characteristic lesions and a typical history. [2, 4]
In children, observation of concurrent gingivostomatitis is almost pathognomonic.
In adults, the presence of occupational risk factors or finding of concurrent oral or genital herpes lesions should strongly suggest the diagnosis.
Definitive diagnostic testing includes the Tzanck test, viral cultures, serum antibody titers, fluorescent antibody testing, or DNA hybridization. Ideally, specimens should be obtained from lesions that have been present less than 24 hours to maximize sensitivity, regardless of the diagnostic modality used.
Viral culture of the aspirated vesicle fluid is the most specific assay and represents the diagnostic criterion standard. This test is usually more costly and time consuming, requiring 24-48 hours, but it does provide the ability to differentiate HSV-1 and HSV-2 infections. Specificity is 100%, with sensitivity ranging from 75% with initial episodes to as low as 50% during recurrences.
Polymerase chain reaction and immunofluorescent microscopy have become more widely available and cost effective.
HSV serologic tests are available but are of limited utility owing to lifelong positivity after initial seroconversion.
The Tzanck test is less commonly performed because of its relatively low sensitivity, but it may be helpful in certain cases. Smears are obtained by scraping the base of an unroofed vesicle. The smears are Giemsa-stained, and a positive test is indicated by light microscopy findings of multinucleated giant cells, often with visible viral inclusions.
Recurrent infections, atypical presentations, or unusual locations should suggest an immunodeficient state. HIV testing should be considered in patients with such presentations. [5, 6]
