PEDIATRIC DERMATOLOGY

What's your DX?

By Bernard A. Cohen, MD

The mother of a 16-month-old boy brings him to your office for evaluation of a painful blistering rash on the tip of his right thumb (Figure 1). The rash began two days ago as a single blister. The boy has no fever or other symptoms, and no other member of the family, including his parents and 3- and 5-year-old siblings, is ill or has a rash.

1. What other history would help you make a diagnosis?

2. How can you confirm your clinical diagnosis?

3. What is your differential diagnosis?

4. How would you treat this child?

Discussion

This toddler has a classic whitlow caused by primary inoculation of herpes simplex virus type 1. Further questioning of his mother revealed that she has recurrent herpes labialis and that the last episode cleared several days before her son developed the rash.

Herpetic whitlow is communicated by direct manual contact with oral or genital lesions. It is seen most commonly in thumb-suckers and nail-biters between 5 months and 6 years old who have oral lesions. In adults it occurs with exogenous occupational or sexual exposure.^1,2 Recurrences are common and have been reported up to several years after the initial attack.³

Skin lesions develop from one day to three weeks after exposure. They consist of painful vesicles clustered on an edematous erythematous base; the vesicles may ulcerate or fuse to form one or more large bullae, as in this boy. Accidental rupture or surgical debridement of the bullae usually yields a clear or straw-colored fluid without pus.

Diagnosis. A Tzanck smear can be used to confirm the clinical diagnosis. To obtain a smear, unroof one of the blisters with a #15 blade. Gently scrape the base of the blister and spread the contents on a glass slide. After drying and fixing in ethanol, the slide is prepared with Wright-Giemsa stain and examined for the presence of characteristic multinucleated giant cells (Figure 2). Some pediatricians will want to send the smear to a pathologist for preparation and reading, or refer the patient to a dermatologist for the procedure.

Unfortunately, Tzanck smears are positive only about two thirds of the time even when read by experienced pathologists. Definitive diagnosis may require viral culture of vesicle fluid, which takes from 12 to 48 hours. Serologic studies to demonstrate antibodies to HSV 1 or HSV 2 are of little value in acute infection, and only provide evidence of past viral exposure. It is now possible to do specific double-fluorescent antibody tests and polymerase chain reaction studies to get a rapid and reliable laboratory confirmation.

The differential. Herpetic whitlow can be confused with painful bacterial dactylitis or paronychia, which is usually caused by group A streptococcus or Staphylococcus aureus. Both of these organisms produce a few large pustules that yield pus and gram-positive organisms on Gram-stained smears. Bacterial cultures confirm the diagnosis.

In viral-induced hand-foot-and-mouth syndrome, the vesicles are characteristically oval and sit on a red base giving a solar flare effect. The lesions are often asymptomatic and symmetric on the hands and feet; vesicles or erosions are usually found on the palate as well.

Acute contact dermatitis can appear as blistering on the hands. The vesicles and bullae are usually intensely itchy rather than painful, unless infected. Bacterial and viral studies are negative.

Treatment. Unfortunately, by the time the diagnosis is considered, lesions are usually fully blossomed. The response to antiviral therapy varies. Untreated herpetic whitlow can take two to four weeks to resolve.^1­4 Anecdotal reports suggest that oral acyclovir, 200 mg five times a day for 10 days, can shorten healing time.^4,5 Several new antiviral agents, including valacyclovir and famciclovir, have good activity against herpes simplex viruses and are better absorbed in the gastrointestinal tract than acyclovir, allowing three divided daily doses. However, neither of these drugs is approved yet for use in children. There is no evidence that topical antiviral preparations are of any value in treating whitlow.

Painful vesicles and erosions should be treated with cool compresses, and with topical or oral antibiotics when secondary bacterial infection is suspected. Acetaminophen or ibuprofen may be given for pain or fever.

THE AUTHOR is Director, Pediatric Dermatology and Cutaneous Laser Center, and Associate Professor of Pediatrics and Dermatology at Johns Hopkins University School of Medicine, Baltimore. He is a Contributing Editor for Contemporary Pediatrics.

REFERENCES

1. Feder HM Jr, Long SS: Herpetic whitlow: Epidemiology, clinical characteristics, diagnosis, and treatment. Am J Dis Child 1983;137:861

2. Walker LG, Simmons BP, Lovallo JL: Pediatric herpetic hand infections. J Hand Surg (Am) 1990;15:176

3. Sehayik RI, Bassett F III: Herpes simplex infection involving the hand. Clin Orthop 1982;166:138

4. Schwandt NW, Mjoe DP, Lubow RM: Acyclovir and treatment of herpetic whitlow. Oral Surg Med Oral Pathol 1987;64:255

5. Jue SJ, Whitley RJ: Herpes simplex virus infections, in Gellis and Kagan's Current Pediatric Therapy, ed 15, Burg FD, Wald ER, Ingelfinger JF, Polin RA (eds). Philadelphia, WB Saunders, 1996, pp 642­645

Bernard Cohen. Pediatric Dermatology: What's your DX?. Contemporary Pediatrics 2000;1:37.