Now where did he get that big blister?

The Case

You are called to the emergency department (ED) to evaluate a 15-month-old child with a "burn" on his foot. His mother reports that when she arrived home from work today, she found her son sleeping in his crib with one of his old sneakers on his right foot. After a few hours, a small patch of redness had progressed into a large blister on his right great toe. He is fussy and is not bearing any weight on the right foot.

Diagnosis: Friction blister

PATHOPHYSIOLOGY

Friction blisters result from mechanical separation of epidermal cells in the midepidermis and the filling of the space with plasma.¹ They are more likely to occur on areas where the epidermis is thick and tightly tethered to underlying structures, particularly the palms, soles, fingers, and toes.

Friction blisters are a common problem in settings where the foot is subject to recurrent or persistent trauma. Blisters, erosions, and crusts are commonly found on the dorsal surfaces of the distal phalanges of infants who spend long periods of time in a prone position and whose feet and toes chronically rub against the isolette bed sheets.

They also are a recurrent problem in long-distance runners, figure skaters, ice hockey players, and other athletes whose feet sustain significant friction injuries, particularly in dry or excessively moist, warm environments.² The tips of the toes, sides of the feet, and backs of the heels are especially prone to this injury.

A survey of deployed soldiers in a desert environment showed that foot problems were a significant cause of medical disability; friction blisters accounted for more than 40% of foot complaints.³ In these settings, properly fitted foot wear and cushioning socks can reduce the risk of friction injury and the development of bullae.

DIFFERENTIAL DIAGNOSIS

Friction blisters in children should not be confused with ischemic injuries such as those associated with pressure sores, diabetic blisters, and ligature injuries, which can progress to necrosis and full-thickness ulceration.

The differential diagnosis would also include accidental and nonaccidental thermal and chemical burns resulting in partial- or full-thickness skin necrosis with painful bullae, erosions, and ulcerations on an irregularly shaped red base. The distribution of the bullae-not affecting the top of the toe nor adjacent toes-makes an immersion burn an unlikely if not implausible mechanism. Painful herpetic vesicles may fuse to form large bullae, but the distinctive loculations are often visible within the bullae.

Blistering associated with enteroviral infections and chicken pox is usually readily distinguished from friction- and pressure-induced blisters. Autoimmune bullous disorders, fixed drug reactions, erythema multiforme, and other primary dermatologic disorders also present with distinctive clinical and histologic findings.⁴

TREATMENT

In general, large blisters should not be popped. The risk of infection increases when the skin is not intact.⁵ Time will resolve the condition, although oral antibiotics could be considered if there is concern for superinfection.

OUR PATIENT

According to our patient's baby sitter, she placed the old shoes on the child before putting him down for a nap. He kicked off the left shoe, but the right shoe stayed in place. His mother couldn't believe that the sitter hadn't found the new shoes in the closet.

The bulla did not rupture and was nearly gone 3 days later. His mother put his old shoes in the trash so that the sitter would be sure to use the newer, appropriately sized shoes.

DR KRUGMAN is chairman, Department of Pediatrics, MedStar Franklin Square Medical Center, Baltimore, Maryland. DR COHEN, the section editor for Dermatology: What's Your Dx? is director, Pediatric Dermatology and Cutaneous Laser Center, and associate professor of pediatrics and dermatology, Johns Hopkins University School of Medicine, Baltimore. The author and section editor have nothing to disclose regarding affiliation with or financial interest in any organization that may have an interest in any part of this article. Vignettes are based on real cases that have been modified to allow the author and editor to focus on key teaching points. Images may also be edited or substituted for teaching purposes.

REFERENCES

1. Knapik JJ, Reynolds KL, Duplantis KL, Jones BH. Friction blisters. Pathophysiology, prevention and treatment. Sports Med. 1995;20(3):136-147.

2. Tlougan BE, Mancini AJ, Mandell JA, Cohen DE, Sanchez MR. Skin conditions in figure skaters, ice-hockey players and speed skaters: part I-mechanical dermatoses. Sports Med. 2011;41(9):709-719.

3. Cramer JS, Forrest K. A survey of deployed foot problems in a desert environment. Mil Med. 2008;173(4):359-361.

4. Sprecher E. Epidermolysis bullosa simplex. Dermatol Clin. 2010;28(1): 23-32.

5. Swain AH, Azadian BS, Wakeley CJ, Shakespeare PG. Management of blisters in minor burns. Br Med J (Clin Res Ed). 1987;295(6591):181.