Swollen, purple, blistered thumb leads to diagnosis of herpetic whitlow

Swollen, purple, blistered thumb leads to diagnosis of herpetic whitlow | Image credit: Author provided

You are asked to evaluate a boy, aged 14 years, who presents with one week of tender, expanding, confluent, purple blisters on his swollen left thumb, extending under the thumbnail. What is the diagnosis?

Diagnosis

Herpetic whitlow

The Case

A boy, aged 14 years, initially presented to the emergency department with left hand swelling, burning pain, itchiness, and erythema, which he had experienced for 3 days. The thumb had several vesicular lesions near the lateral edge of the fingertip. There were no other notable findings on physical examination. A complete blood count was negative for leukocytosis, and results of an x-ray of the left hand were benign with no bone involvement. Orthopedics had been consulted, and after discussion the patient was discharged with topical terbinafine cream to treat a possible fungal infection. He returned to the same emergency department 4 days later with worsening symptoms. The thumb lesions had expanded and become confluent, with blisters now extending under his thumbnail.

His mother reported application of the terbinafine cream to the finger as prescribed. The burning pain went away after a couple of days; however, the swelling and discoloration worsened, so they returned for reevaluation. The patient reported that washing the finger with soap and hot water mildly relieved his symptoms, but they soon returned. The lesion showed hemorrhagic confluent vesicles that were tender on palpation. Full medical examination was otherwise unremarkable except for a small healing vesicle on the right lower lip, and the patient was unsure whether his surgical mask had been removed for facial examination at the last visit.

Differential diagnosis

Several conditions, ranging from benign to severe, can cause a swollen finger in an adolescent. Most are clinical diagnoses that necessitate timely, accurate decision-making to initiate proper treatment. Initially considering infections that require early intervention is important in preventing more serious complications. Some common etiologies are outlined in the Table.

Bacterial infections of either the nail folds (paronychia) or the fleshy portion of the fingertip (felon) are typically the result of trauma.¹ This can be identified with thorough history taking and/or physical exam signs, such as significant bruising or a fracture/dislocation of 1 or more fingers. For younger children, inquiring about their typical activities or any unsupervised play can be helpful in the absence of witnessed trauma. Habits such as sucking or chewing of the digits, especially in young children, point toward an infectious etiology. Sick contacts increase suspicion of a viral etiology. For example, other children with similar symptoms could indicate coxsackievirus,² and history of herpes simplex virus (HSV) in a caretaker could indicate herpetic whitlow.³ Other important signs include a history of such lesions, change in appearance of the lesion, and associated symptoms such as fever, weight loss, or rashes elsewhere on the skin.

Once an infectious etiology is suspected, the differential diagnosis must be narrowed further to ensure efficacious treatment. Features such as erythema, pruritus, edema, and pain are common across diagnoses, so identifying unique signs is crucial for differentiation. Paronychia is typically confined to the nail bed and will not extend to the finger pad or down the length of the finger, even in chronic cases involving multiple digits.¹ Likewise, a felon does not extend beyond the distal interphalangeal joint and is typically localized to the fleshy portion of the fingertip.¹ Herpetic whitlow demonstrates a characteristic vesicular pattern, but after several days vesicles commonly combine and form a larger, necrotic, bullous lesion. Careful inspection of edema can be helpful in differentiation, as the flesh will be significantly tense in a felon while remaining soft in herpetic whitlow.¹ Hand-foot-and-mouth disease, caused by coxsackievirus, also presents with vesicular lesions on the hands that can become hemorrhagic, purple, or bullous. Similar lesions are seen on the feet, along with painful lesions in the mouth, as opposed to lesions on the lip seen in oral herpes infection.² Basic lab studies are not often necessary but may be helpful if clinical signs are not obvious. Notably, polymerase chain reaction (PCR) testing for HSV of a sample from an unroofed vesicle can rule out herpetic whitlow or other viral blisters such as coxsackie.^1,3

Several noninfectious causes should be considered in the differential diagnosis as well, many of which mimic the findings described above. This often involves immunologically mediated reactions, such as dyshidrotic eczema. Like herpetic whitlow, this is a vesicular eruption that can trigger burning pain but more commonly presents with pruritus.¹ Typically, these lesions are more extensive, often bilateral, and may form fluid-filled bullae.⁴ At presentation they are often noted on multiple body regions, typically hands and feet but extending proximally along upper and lower extremities.⁴ Other considerations include contact/irritant dermatitis or a foreign body reaction. Contact dermatitis typically involves a larger region as well.^1,5 For these, careful examination for a foreign body and history taking for allergen/irritant exposure or trauma, respectively, are key. Although much less common, local neoplasms, such as a pyogenic granuloma or a metastatic lesion, are also possible.⁴ These lesions are often more chronic and may have associated symptoms (ie, weight loss or cachexia in metastatic lesions).

Herpetic whitlow

Herpetic whitlow refers to a superficial skin infection due to HSV, traditionally located on the fingers.³ Still, cutaneous HSV can affect various regions of the body, including the palmar surface, arms, and toes.⁶ It is most common within a bimodal age distribution, typically affecting infants or young adults.³ It is transmitted through direct skin-to-skin contact, and the majority of cases in children are due to HSV-1,³ the most common cause of oral herpes, also known as herpes labialis.⁷ However, it can also be caused by HSV-2,³ which causes most genital HSV infections.⁷ The most common presentations are young children with oral herpes who autoinoculate through sucking on fingers or toes, or in health care workers such as dentists who physically contact the mouth of an individual with oral herpes.³ Given various potential routes of transmission, it would be prudent to inquire about sexual activity in adolescents and adults, especially in the absence of exposure to an individual with oral HSV infection.

The initial presentation of herpetic whitlow is 1 or more vesicles that may be clear or yellow in color with surrounding erythema.³ They are often accompanied by numbness and tingling, burning pain, and/or pruritus of the affected region.⁶ Over time, vesicles may coalesce, satellite lesions may appear, and the site may become hemorrhagic or otherwise discolored.³ Initial pain typically abates but edema, erythema, and pruritus may continue until resolution of the lesions.³ Systemic features such as fever, lymphangitis, or regional lymphadenopathy have also been noted.⁶ These may be signs of a complication, the most common being bacterial superinfection, typically with Staphylococcus aureus.³ This can lead to impetigo, cellulitis, or abscess formation, which require antibiotic therapy.^1,3 Other complications are uncommon, though very rare findings, including meningitis, have been noted.⁸

Laboratory testing for herpetic whitlow does not necessarily need to be performed but can be helpful in confirming the diagnosis. The gold standard for this is PCR testing from an unroofed vesicle, which is the most sensitive diagnostic test and also allows for HSV typing.³ Other options include serology, Tzanck test, or lesion antigen detection, although these are less often used.^1,3 Other studies, such as complete blood count, a metabolic profile, or C-reactive protein may be of use when considering other infectious etiologies or bacterial superinfection.⁹ Imaging is typically not necessary, though ultrasound is useful for abscess evaluation.⁹ 

Treatment of herpetic whitlow varies with presentation and clinical judgment. The infection is typically self-limited and most cases resolve in 2 to 4 weeks.¹ Oral antiviral medications such as acyclovir or valacyclovir have been utilized for decades with significant success.³ These medications are relatively well tolerated with few adverse effects, and short-term use rarely leads to resistant HSV strains.¹⁰ They are especially useful for lesions present for less than 48 hours, recurrent lesions, or in immunocompromised patients.¹ There is no particular consensus for length of therapy.¹ Studies show infection recurrence in about 1 in every 4 to 5 cases.⁸ Patients and/or family members should also be educated about HSV and its spread to reduce risk of recurrence and transmission to others. Keeping the lesions clean and dry is key to preventing bacterial superinfection.¹ Incision and drainage should not be performed except in rare cases of secondary abscess formation; they increase the risk of superinfection.^1,3 Finally, it may be helpful to involve specialty services, including dermatology, orthopedics, and plastic surgery, depending on the severity and complexity of the infection.⁸

Case outcome

PCR testing was performed on the patient’s finger on an unroofed vesicle, which was positive for HSV-1. Use of the terbinafine cream was discontinued, and the patient was started on a course of oral valacyclovir. The lesion showed dramatic improvement over the following 24 to 48 hours. The patient and his family continued with cool compresses throughout the day and acetaminophen as needed during the following week. The lesion resolved and has not returned. They will follow up with their primary care provider for evaluation of the thumb and discussion of HSV and its potential complications.

Click here to read more from the June, 2023 issue of Contemporary Pediatrics®.

References:

1. Rerucha CM, Ewing JT, Oppenlander KE, Cowan WC. Acute hand infections. Am Fam Physician. 2019;99(4):228-236.

2. Saguil A, Kane SF, Lauters R, Mercado MG. Hand-foot-and-mouth disease: rapid evidence review. Am Fam Physician. 2019;100(7):408-414.

3. Rubright JH, Shafritz AB. The herpetic whitlow. J Hand Surg Am. 2011;36(2):340-342. doi:10.1016/j.jhsa.2010.10.014

4. Calle Sarmiento PM, Chango Azanza JJ. Dyshidrotic eczema: a common cause of palmar dermatitis. Cureus. 2020;12(10):e10839. doi:10.7759/cureus.10839

5. Nassau S, Fonacier L. Allergic contact dermatitis. Med Clin North Am. 2020;104(1):61-76. doi:10.1016/j.mcna.2019.08.012

6. Lieberman L, Castro D, Bhatt A, Guyer F. Case report: palmar herpetic whitlow and forearm lymphangitis in a 10-year-old female. BMC Pediatr. 2019;19(1):450.
doi:10.1186/s12887-019-1828-5

7. Cole S. Herpes simplex virus: epidemiology, diagnosis, and treatment. Nurs Clin North Am. 2020;55(3):337-345. doi:10.1016/j.cnur.2020.05.004

8. Lopez-Delgado D, Fernandez-Pugnaire MA, Ruiz-Villaverde R. Multiple grouped papules and vesicles on the finger of a 2-year-old girl. J Paediatr Child Health. 2018;54(3):332. doi:10.1111/jpc.2_13868

9. Silverberg B. A structured approach to skin and soft tissue infections (SSTIs) in an ambulatory setting. Clin Pract. 2021;11(1):65-74. doi:10.3390/clinpract11010011

10. Whitley R, Baines J. Clinical management of herpes simplex virus infections: past, present, and future. F1000Res. 2018;7:F1000 Faculty Rev-1726. doi:10.12688/f1000research.16157.1