Proximal nail fold swelling, pain, and granulation tissue.

A 28-year-old man presented with a 4-month history of left great toe pain, swelling, erythema, and drainage. The patient was previously treated with a topical antifungal, oral antibiotics, and hot water soaks without improvement of symptoms. The patient's toe upon presentation is depicted in Fig 1 and after gentle washing in Fig 2. The patient's nail plate is depicted in Fig 3.

Fig 1

Fig 2

Fig 3

Question 1. What is the diagnosis?

Acute paronychia

Onychomycosis

Retronychia

Squamous cell carcinoma

Ingrown nail

Answers

Acute paronychia – Incorrect. Acute paronychia is caused by a disruption in the seal of the nail fold and nail plate allowing often polymicrobial infections to develop in the local periungual soft tissues.

Onychomycosis – Incorrect. While onychomycosis can cause proximal onycholysis, it typically does not cause periungual inflammation and drainage.

Retronychia – Correct. The diagnosis of retronychia is made clinically. Criteria for diagnosis are chronic inflammation of the proximal nail fold, granulation tissue protruding from under the proximal nail fold, and thickened often doubled proximal nail plate. Retronychia occurs when the nail plate separates completely from the matrix and a new plate grows under the old plate. This pushes the nail plate upwards and causes inflammation to the proximal nail fold.1, 2, 3, 4, 5

Squamous cell carcinoma – Incorrect. Although the presentation of squamous cell carcinoma varies, it typically appears as a periungual friable, verrucous mass with associated nail dystrophy.

Ingrown nail – Incorrect. Ingrown nails occur along the medial or lateral border of the nail fold. This patient's symptoms occurred at the proximal nail fold.

Question 2. What is the recommended treatment for retronychia?

Topical steroids

Topical antifungals

Oral antibiotics

Partial nail plate avulsion

Total or proximal nail plate avulsion

Answers

Topical steroids – Incorrect. Topical steroids might decrease local inflammation but will not stop the foreign body reaction of the proximal nail fold to the ingrowing nail plate.

Topical antifungals – Incorrect. Antifungals will not address the underlying cause of retronychia.

Oral antibiotics – Incorrect. Although a bacterial infection might develop secondarily to a retronychia, antibiotics will not address the underlying cause of retronychia.

Partial nail plate avulsion – Incorrect. Total nail plate avulsion is the recommended treatment.

Total or proximal nail plate avulsion – Correct. Retronychia resolves with total nail plate or proximal nail plate avulsion.1, 2, 3, 4, 5 Diagnosis is confirmed by the presence of a double nail and observation of normal nail growth after nail plate avulsion.1, 2, 3, 4, 5

Question 3. What is the underlying pathologic mechanisms contributing to retronychia?

Proximal nail fold trauma

Irritant dermatitis

Chronic fungal infection

Chronic bacterial infection

Nail matrix trauma

Answers

Proximal nail fold trauma – Incorrect. Although the proximal nail fold suffers trauma in retronychia due to a proximally growing nail plate, trauma to the proximal nail fold is not what causes a retronychia to develop.

Irritant dermatitis – Incorrect. Although irritant dermatitis is a common cause of chronic paronychia, it is not responsible for retronychia.

Chronic fungal infection – Incorrect. Fungal infection is not associated with retronychia.

Chronic bacterial infection – Incorrect. Bacterial infection might develop secondary to the disruption of the seal of the proximal nail fold and nail plate due to trauma from the ingrowing nail plate; however, it is not the cause of the proximally growing nail plate.

Nail matrix trauma – Correct. Retronychia occurs secondary to minor physical trauma to the nail matrix often from the distal free edge of the nail plate being pushed backwards into the nail matrix, as would happen with long nails or with poor fitting footwear. The traumatic event might be a singular event, such as a stubbed toe, or might occur from repetitive trauma as one might experience with jogging, dancing, or wearing tight-fitting shoes.1, 5 After the traumatic event occurs, the nail plate separates completely from the nail matrix, and a new plate grows under the old plate. This growth results in the old plate pushing up into the proximal nail fold, causing inflammation at the proximal nail fold. In addition, the distal nail plate becomes more adherent and, in this case, was noticeably more difficult to elevate than a typical nail plate avulsion with a Freer elevator. The length the patient's toe nails and his report of tight-fitting boots support the diagnosis of retronychia through repetitive trauma. In addition, the patient has multiple Beau lines on his second toenail which is a clue that the patient's nail matrices have experienced repetitive trauma.