(See also Overview of Nail Disorders Overview of Nail Disorders A variety of disorders can affect nails, including deformities, trauma, infections of the nail, paronychia, retronychia, and ingrown toenails. Nail changes may occur in many systemic conditions... read more .)
Paronychia is usually acute, but chronic cases Chronic Paronychia Chronic paronychia is recurrent or persistent nail fold inflammation, typically of the fingers. (See also Overview of Nail Disorders.) Chronic paronychia is an inflammatory disorder of the nail... read more 
occur. In acute paronychia, the causative organisms are usually Staphylococcus aureus or streptococci and, less commonly, Pseudomonas or Proteus species. Organisms enter through a break in the epidermis resulting from a hangnail, trauma to a nail fold, loss of the cuticle, or chronic irritation (eg, resulting from water and detergents). Biting or sucking the fingers can also predispose people to developing the infection. In toes, infection often begins at an ingrown toenail Ingrown Toenail An ingrown toenail is incurvation or impingement of a nail border into its adjacent nail fold, causing pain. (See also Overview of Nail Disorders.) Causes of ingrown toenail include tight shoes... read more 
.
Novel drug therapies, such as with inhibitors of epidermal growth factor receptor (EGFR), mammalian target of rapamycin (mTOR), and less commonly BRAF gene inhibitors, can cause paronychia along with other skin changes. The mechanism is not completely understood. However, most cases seem to be caused by the drug itself, such as through alterations in retinoic acid metabolism, and not by secondary infection.
In patients with diabetes and those with peripheral vascular disease Peripheral Arterial Disease Peripheral arterial disease (PAD) is atherosclerosis of the extremities (virtually always lower) causing ischemia. Mild PAD may be asymptomatic or cause intermittent claudication; severe PAD... read more 
, toe paronychia can lead to more extensive infection and threaten the limb.
Symptoms and Signs
Paronychia develops along the nail margin (lateral and/or proximal nail fold), manifesting over hours to days with pain, warmth, redness, and swelling. Pus usually develops along the nail margin and sometimes beneath the nail. Infection can spread to the fingertip pulp, causing a felon Felon A felon is an infection of the pulp space of the fingertip, usually with staphylococci and streptococci. (See also Overview and Evaluation of Hand Disorders.) The most common site is the distal... read more 
. Rarely, infection penetrates deep into the finger, sometimes causing infectious flexor tenosynovitis Infectious Flexor Tenosynovitis Infectious flexor tenosynovitis is an acute infection within the flexor tendon sheath. Diagnosis is suggested by Kanavel signs and confirmed with x-rays. Treatment is surgical drainage and antibiotics... read more .
Diagnosis
Clinical evaluation
Diagnosis of acute paronychia is by clinical evaluation.
Several skin conditions can cause changes that mimic paronychia and should be considered, particularly when treatment is not effective initially. These conditions include squamous cell carcinoma Squamous Cell Carcinoma Squamous cell carcinoma is a malignant tumor of epidermal keratinocytes that invades the dermis; this cancer usually occurs in sun-exposed areas. Local destruction may be extensive, and metastases... read more 
, proximal onychomycosis Onychomycosis Onychomycosis is fungal infection of the nail plate, nail bed, or both. The nails typically are deformed and discolored white or yellow. Diagnosis is by appearance, wet mount, culture, polymerase... read more 
, pyogenic granuloma Pyogenic Granulomas Pyogenic granulomas are fleshy, moist or crusty, usually scarlet vascular nodules composed of proliferating capillaries in an edematous stroma. The lesion, composed of vascular tissue, is neither... read more 
, pyoderma gangrenosum Pyoderma Gangrenosum Pyoderma gangrenosum is a chronic, neutrophilic, progressive skin necrosis of unknown etiology often associated with systemic illness and sometimes skin injury. Diagnosis is clinical. Treatment... read more 
, and herpetic whitlow Herpetic Whitlow Herpetic whitlow is a cutaneous infection of the distal aspect of the finger caused by herpes simplex virus. (See also Overview and Evaluation of Hand Disorders.) Herpetic whitlow may cause... read more 
.
Treatment
Antibiotics effective against staphylococci and streptococci
Drainage of pus
Early treatment is warm compresses or soaks and an oral antibiotic effective against staphylococci and streptococci (eg, dicloxacillin or cephalexin 250 mg 4 times a day, clindamycin 300 mg 4 times a day). In areas where methicillin-resistant S. aureus is common, antibiotics that are effective against this organism (eg, trimethoprim/sulfamethoxazole) should be chosen based on results of local sensitivity testing. In patients with diabetes and others with peripheral vascular disease, toe paronychia should be monitored for signs of cellulitis Cellulitis Cellulitis is acute bacterial infection of the skin and subcutaneous tissue most often caused by streptococci or staphylococci. Symptoms and signs are pain, warmth, rapidly spreading erythema... read more 
or more severe infection (eg, extension of edema or erythema, lymphadenopathy, fever).
Fluctuant swelling or visible pus should be drained with a Freer elevator, small hemostat, or #11 scalpel blade inserted between the nail and nail fold. Skin incision is unnecessary. A thin gauze wick can be inserted for 24 to 48 hours to allow drainage.
A case caused by epidermal growth factor receptor inhibitor therapy and refractory to the usual treatments was treated successfully with autologous platelet-rich plasma.
Key Points
Acute paronychia can be related to a hangnail, nail fold trauma, loss of the cuticle, chronic irritation, or biting or sucking of the fingers.
The diagnosis is likely when severe redness, pain, and warmth develop acutely along the nail margin, but consider alternative diagnoses, particularly if treatment is unsuccessful.
Treat with an antibiotic and moist heat and by draining any visible pus.
