(See also Overview of Nail Disorders.)
Paronychia is usually acute, but chronic cases 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.
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, toe paronychia can lead to more extensive infection and threaten the limb.
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. Rarely, infection penetrates deep into the finger, sometimes causing infectious flexor tenosynovitis.
Diagnosis of acute paronychia is by clinical evaluation.
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 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.
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.