Description

• Superficial inflammation of the lateral and posterior nail folds surrounding the fingernail or toenail. Develops after breakdown of barrier between nail plate and the adjacent nail fold
• Acute: characterized by pain, erythema, and swelling (1) lasting <6 weeks; usually a bacterial infection appearing after nail biting, trauma, manicures, ingrown nails, and hangnail manipulation. It also occurs as an adverse effect from several drugs. It can progress to abscess formation.
• Chronic: characterized by swelling, tenderness, cuticle elevation, and nail dystrophy and separation lasting at least 6 weeks, or recurrent episodes of acute eponychial inflammation and drainage
• Chemotherapy-associated paronychia (CAP) starts 4 to 8 weeks after chemotherapy initiation (2).
• May be considered work-related among bartenders, restaurant servers, dishwashers, nurses, and others who often wash their hands
• Usually involves one finger but drug-induced paronychia may involve multiple fingers
• Relevant anatomy: nail bed, nail plate, and perionychium
• Synonym(s): eponychia, perionychia, retronychia

Pediatric Considerations
Less common in pediatric age groups; commonly caused by trauma to periungual skin, such as thumb/finger-sucking or other injuries (Staphylococcus aureus and group A Streptococcus may be present). Paronychia is also a frequent adverse effect of BRAF and MEK inhibitor anticancer drugs.

Epidemiology

Incidence

• One of the most common hand infections in the United States
• Predominant age: all ages
• Predominant sex: female > male

Etiology and Pathophysiology

• Acute: mixed aerobic and anaerobic bacterial flora in 50% of cases. Staphylococcus aureus most common and Streptococcus pyogenes; less frequently, Pseudomonas aeruginosa and other gram-negative bacteria (with chronic paronychia)
• Chronic: eczematous reaction with secondary Candida albicans (~95%)
• Pediatric age groups: mixed anaerobic (Fusobacterium, Peptostreptococcus) and aerobic infections (Eikenella corrodens, S. aureus, streptococci) from oral flora
• A paronychial infection commonly starts in the lateral nail fold.
• Acute paronychia of the fingers is often due to trauma; acute paronychia of the toes is often due to ingrown nails (3).
• Recurrent inflammation, persistent edema, and fibrosis of nail folds cause nail folds to round up and retract, exposing nail grooves to irritants, allergens, and pathogens.
• Inflammation compromises ability of proximal nail fold to regenerate cuticle leading to decreased vascular supply. This can cause decrease efficacy of topical medications.
• Early in the course, cellulitis alone may be present.
• An abscess can form if the infection does not resolve quickly.

Risk Factors

• Acute: direct or indirect trauma to cuticle or nail fold, manicured/sculptured nails, nail biting, thumb sucking, manipulating a hangnail, ingrown toenail
• Chronic: frequent immersion of hands in water with excoriation of the lateral nail fold (e.g., chefs, bartenders, housekeepers, swimmers, dishwashers, nurses)
• Predisposing conditions such as diabetes mellitus (DM) and immunosuppression
• Medications such as EGFR inhibitors, systemic retinoids, chemotherapy, and antiretroviral agents

General Prevention

• Acute: Avoid trauma such as nail biting or manipulating a hangnail. Prevent ingrown toenails.
• Chronic: Avoid exposure to allergens and contact irritants; keep fingers/hands dry; wear rubber gloves with a cotton liner. Prevent excoriation of the skin.
• Keep nails short; avoid manicures.
• Apply moisturizer after washing hands.

Commonly Associated Conditions

DM, eczema or atopic dermatitis, immunosuppression