Nail Infections

Nail Infections Overview - Nailing the Basics

• Key Nail Structures:
  • Nail Plate: Hard keratin, often invaded.
  • Nail Bed: Tissue under plate, common infection site.
  • Nail Matrix: Growth origin; damage impacts nail integrity.
  • Nail Folds (Perionychium): Skin surrounding nail; site of paronychia.
• Major Infection Categories:
  • Onychomycosis: Fungal (e.g., Trichophyton rubrum). Most prevalent.
  • Paronychia: Bacterial (acute) or fungal (chronic) inflammation of nail folds.
  • Pseudomonas: Bacterial, causes green nail syndrome (chloronychia).
  • Viral: e.g., Herpetic whitlow, periungual warts.

⭐ Onychomycosis accounts for approximately 50% of all nail disorders and 90% of toenail infections globally, with dermatophytes being the primary culprits.

Onychomycosis - Fungal Foes

• Definition: Fungal infection of nail unit (plate, bed, matrix).
• Etiology:
  • Dermatophytes (~90%): Trichophyton rubrum (most common), T. mentagrophytes.
  • Yeasts: Candida albicans (esp. chronic paronychia).
  • Non-Dermatophyte Molds (NDMs): Scopulariopsis, Aspergillus.
• Clinical Types:
  • Distal Lateral Subungual (DLSO): Most common; subungual hyperkeratosis, onycholysis.
  • Proximal Subungual (PSO): Marker for immunosuppression (e.g., HIV).
  • White Superficial (WSO): Chalky white patches on nail surface; T. mentagrophytes.
  • Endonyx: Invades nail plate interior.
  • Total Dystrophic: End-stage; complete nail destruction.
• Diagnosis:
  • KOH microscopy: Visualizes hyphae.
  • Fungal culture: Gold standard.
  • Nail biopsy + PAS stain: High sensitivity.
• Management:
  • Topical (mild, <50% nail, no matrix): Ciclopirox, Amorolfine, Efinaconazole.
  • Systemic:
    • Terbinafine (DOC for dermatophytes): 250 mg/day (Fingernails: 6 wks; Toenails: 12 wks).
    • Itraconazole: Pulse (200 mg BID, 1 wk/month; Fingernails: 2 pulses; Toenails: 3 pulses).
  • Adjunct: Debridement.

⭐ Proximal Subungual Onychomycosis (PSO) is strongly associated with HIV infection and can be an early indicator of immunosuppression.

Paronychia - Peril at the Periphery

• Inflammation of nail folds (periungual tissue).
• Acute Paronychia:
  • Sudden onset, painful, erythematous, swollen nail fold.
  • Causative organisms: Staphylococcus aureus (most common), Streptococcus pyogenes.
  • Trauma (nail biting, manicures, hangnails) is a common predisposing factor.
  • Management: Warm compresses, topical/oral antibiotics. Incision & drainage if abscess forms.
• Chronic Paronychia:
  • Insidious onset, > 6 weeks duration, boggy, tender nail folds, cuticle loss.
  • Causative organisms: Candida albicans (most common), irritant/allergic contact dermatitis, Pseudomonas (green discoloration).
  • Occupational (wet work): Bartenders, dishwashers, healthcare workers.
  • Management: Avoid irritants/moisture, topical/systemic antifungals (e.g., topical clotrimazole, oral fluconazole), topical steroids.

⭐ Chronic paronychia is frequently associated with Candida albicans infection, especially in individuals with persistent wet hands or diabetes mellitus. Herpetic whitlow can mimic acute paronychia but presents with vesicles.

Other Infections & DDx - Nail Trouble Lookalikes

• Bacterial:

  • Acute Paronychia: S. aureus, Strep. Pain, redness, swelling.
  • Chronic Paronychia: Candida, Pseudomonas. Boggy folds; green if Pseudomonas.

• Viral:

  • Herpetic Whitlow (HSV): Painful vesicles.

• DDx - Non-Infectious:

  • Psoriasis: Pitting, onycholysis, subungual hyperkeratosis.

  ⭐ "Oil drop" or "salmon patch" sign: pathognomonic for nail Psoriasis.

  • Lichen Planus: Longitudinal ridging, pterygium, thinning, 20-nail dystrophy.
  • Trauma: Subungual hematoma, Beau's lines.
  • Eczema: Nail dystrophy, ridging.
  • Alopecia Areata: Geometric pitting, trachyonychia.
  • Yellow Nail Syndrome: Thick, yellow, slow growth; lymphedema, respiratory.
  • Median Nail Dystrophy: Central canal/groove, fir-tree.
  • Drug-induced: e.g., retinoids, chemo.

High‑Yield Points - ⚡ Biggest Takeaways

• Onychomycosis, fungal nail infection, is most commonly caused by Trichophyton rubrum.
• Distal lateral subungual onychomycosis (DLSO) is the most common clinical presentation.
• Oral terbinafine is preferred first-line treatment for dermatophyte onychomycosis.
• Acute paronychia: typically bacterial (Staphylococcus aureus); Chronic paronychia: often Candida albicans.
• Green nail syndrome (chloronychia) is caused by Pseudomonas aeruginosa infection.
• Herpetic whitlow (HSV infection) can mimic bacterial paronychia.
• Diagnosis of onychomycosis: KOH microscopy and fungal culture of nail clippings_._