Finger and toe infections

Digital infections (i.e., finger infections and toe infections) are common and have a variety of causes. Paronychia is acute or chronic inflammation of the nail folds. In the early stages of disease, acute paronychia is typically treated with topical antibiotics; if an abscess forms, incision and drainage is required. Chronic paronychia is treated with topical steroids and patients are advised to avoid skin irritants. Felons, which are subcutaneous infections of the finger pulp, are managed conservatively with oral antibiotics in the early stages; in the later stages, characterized by abscess formation, incision and drainage is required. Blistering distal dactylitis is a localized superficial bacterial infection of the fingers and is treated with incision and drainage and antibiotics. An ingrown toenail is the abnormal growth of the nail plate into the lateral periungual skin of the nail fold. Placement of cushioning material under the ingrown nail plate may help in the early stages but partial nail avulsion or complete nail excision may become necessary.

See “Tenosynovitis” for infection of the tendon sheath and “Human bites” for clenched-fist bite injury, and “Herpetic whitlow” for infection of the distal finger.

Acute paronychia ^[1][2][3]

• Definition: inflammation of the proximal and/or lateral nail folds of the fingers or toes for < 6 weeks
• Epidemiology ^[2]
  • Most common hand infection in the US
  • ♀ > ♂ (3:1)
• Etiology: : most commonly caused by a bacterial infection (e.g., with Staphylococcus aureus)
• Pathophysiology: trauma to the nail folds (e.g., due to manual work, nail biting, a manicure) → disruption of the barrier between the nail plate and the nail fold → increased susceptibility to bacterial infection
• Clinical features
  • Usually involves only one digit
  • Signs of acute inflammation (e.g., redness, warmth)
  • Skin abscess may be present
  • Absence of nail changes
• Diagnostics ^[2]
  • Clinical diagnosis
  • If an abscess is suspected: soft tissue ultrasound, digital pressure test
• Treatment ^[3][4][5][6]
  • Mild erythema without abscess
    • Warm water soaks for 15 minutes 2–4 times per day ^[4]
    • Topical antibiotics, e.g., mupirocin (off-label) for 7–10 days ^[4][7]
    • Consider adding topical steroids for symptom relief. ^[8]
  • Abscess present
    • Perform acute paronychia incision and drainage.
    • Post-procedure
      • Antibiotics are only required in patients with cellulitis, severe illness, and/or immunocompromise. ^[5][9]
      • Perform warm water soaks for 2–3 days.
  • Overt cellulitis or persistent lesion
    • Initiate oral antibiotics, e.g., cephalexin or TMP/SMX (off-label). ^[2][5][10]
    • If oral pathogens are suspected, options include amoxicillin/clavulanate and clindamycin. ^[2][5][10]
    • See “Antibiotic therapy for soft tissue infections” for severity grading and further options.
  • Tetanus-prone wounds: Administer tetanus prophylaxis.
• Complications
  • Felon
  • Osteomyelitis
  • Chronic paronychia

Acute paronychia incision and drainage ^[1]

1. Obtain informed consent.
2. Soak the digit to soften the eponychium.
3. Perform a digital block as required; see “Procedure” in “Peripheral nerve block.”
4. Using a sharp instrument (e.g., No. 11 blade scalpel, needle tip), lift the eponychium away from the nail matrix.
5. Keep the instrument parallel to the nail and continue to lift the eponychium around the border of the paronychia until all of the pus has been released.
6. Apply antibiotic ointment and an absorbent dressing.

Chronic paronychia ^[2]

• Definition: inflammation of the proximal and/or lateral nail folds of the fingers or toes for > 6 weeks
• Epidemiology: common in occupations with repeated exposure to moisture and/or skin irritants (e.g., bartenders, dish cleaners) ^[11]
• Etiology
  • Most commonly caused by chronic exposure to skin irritants (e.g., household chemicals)
  • Rarely caused by infections
• Pathophysiology: : disruption of the barrier between the nail plate and the nail fold (e.g., due to trauma, skin irritants) → persistent exposure of the nail fold to skin irritants → eczematous inflammatory reaction
• Clinical features
  • Usually involves more than one digit
  • Dystrophic nails (e.g., thickened, discolored)
  • Retraction of the proximal nail fold and loss of the cuticle
  • Signs of acute inflammation (e.g., redness, warmth)
  • Abscess (rare)
• Diagnostics: clinical diagnosis based on symptoms and exposure history ^[2]
• Treatment ^[2][4][12]
  • Avoid skin irritants and keep the area dry.
  • Apply a topical antiinflammatory agent, e.g.:
    • Triamcinolone ^[4]
    • Tacrolimus (off-label) ^[12]
  • Refer patients with refractory chronic paronychias to hand surgery.
• Complications
  • Nail dystrophy
  • Nail loss
  • Acute paronychia

Chronic paronychia affecting a single digit should raise concern for malignancy (e.g., squamous cell carcinoma). ^[2]

• Definition: subcutaneous infection of the distal digital pulp
• Etiology
  • Trauma with secondary infection
  • Progression of untreated paronychia
  • Most common pathogen: Staphylococcus aureus
• Pathophysiology: fingertip puncture wound → bacterial inoculation → closed-space infection of the digital pulp → ischemic necrosis
• Clinical features
  • Commonly affects the thumb or index finger
  • Signs of acute inflammation (e.g., warmth, redness)
  • Tense swelling confined to the digital pulp
  • Progressive, severe throbbing pain exacerbated by the dependent position
  • Fluctuance and spontaneous drainage
• Diagnostics ^[4][5][13]
  • Clinical diagnosis
  • Soft tissue ultrasound if an abscess is suspected
  • Consider x-rays to evaluate for retained foreign bodies. ^[1]
  • Bacterial culture of drained fluid or pus if felon incision and drainage is performed ^[1]
• Treatment ^{[1][5][10][13]}
  • All patients
    • Initiate oral antibiotics with S. aureus coverage, choosing β-lactamase-resistant or MRSA-targeted agents as needed. ^[13]
      • E.g., cephalexin , amoxicillin/clavulanate , or TMP/SMX (off-label) ^[5][10]
      • See “Antibiotic therapy for soft tissue infections” for severity grading and further options.
    • Ensure follow-up with hand surgery for reassessment.
    • Tetanus-prone wounds: Administer tetanus prophylaxis.
  • Abscess present
    • Felon incision and drainage
    • Follow-up with culture results within 2–3 days.
  • Abscess absent: conservative management with warm water soaks and digital elevation
• Complications
  • Soft tissue necrosis
  • Septic arthritis
  • Osteomyelitis
  • Flexor tenosynovitis

Felon incision and drainage ^[1]

Due to the risk of complications such as destabilizing the fingertip, loss of function, or amputation, consider early hand surgery consult for difficult cases.

1. Obtain informed consent.
2. Perform a digital block as required; see “Procedure” in “Peripheral nerve block.”
3. Apply a finger tourniquet.
4. Identify the area of maximal fluctuance (must be at least 3 mm distal to the DIP).
5. Make a longitudinal incision parallel to the nail plate.
6. Avoid extension of the incision to the distal interphalangeal crease.
7. Bluntly dissect with a hemostat to break up loculations.
8. Irrigate the wound.
9. Pack the wound with gauze.
10. Place an absorbent dressing over the wound and splint the finger.

• Definition: localized superficial bacterial infection of the fingers
• Epidemiology: more common in children
• Etiology:
  • Open wounds (e.g., trauma, insect bites)
  • Pathogen: group A hemolytic streptococci (most common), staphylococcus aureus
• Clinical features: most frequently affects the volar fat pad of the distal phalanx
  • Single (most common) or multiple purulent blisters (1–2 cm)
  • Usually nontender
• Diagnostics:
  • Clinical diagnosis
  • Gram stain and bacterial culture of the blister fluid
• Treatment: incision, drainage, and oral β-lactamase-resistant antibiotics (e.g., cephalexin or oxacillin)

• Definition: herpes simplex virus (HSV) infection of the distal phalanx
• Clinical features
  • Pain and paresthesia in the finger before the development of vesicles
  • Formation of nonpurulent vesicles over the pulp of the finger
• For further information, see “Herpetic whitlow” in “Herpes simplex virus infections.”

• Definition: abnormal growth of the nail plate into the lateral periungual skin, resulting in an inflammatory foreign body reaction with the risk of subsequent infection
• Epidemiology
  • Prevalence: 2.5–5% of the US population ^[16]
  • More common in adolescents and young adults
  • Sex: ♂ > ♀ (2:1)
• Etiology
  • Extrinsic risk factors: improper nail trimming (most common), tight-fitting shoes, repetitive trauma, hyperhidrosis, and certain medications (e.g., EGFR inhibitors)
  • Intrinsic risk factors: abnormal nail shape and other anatomical abnormalities
  • Secondary infection is most frequently caused by Staphylococcus aureus
• Pathogenesis: excessive nail trimming → formation of a spicule that pierces the lateral nail sulcus → inflammatory foreign body reaction → granulation tissue and disruption of the cutaneous barrier → infection
• Clinical features: the hallux toenails are most commonly affected
  • Inflammatory signs with difficulty walking
  • Hypertrophic granulation tissue
  • Abscess formation and purulent drainage in case of secondary infection
• Diagnostics: clinical diagnosis
• Treatment and prevention
  • Preventive measures: adequate trimming of the nails, proper footwear, and good foot hygiene
  • Conservative measures
    • For lesions with mild inflammatory signs
    • Placement of different materials (cotton, gutter) under the ingrown nail plate to reduce the contact between the nail plate and the nail fold
  • Surgical measures
    • For recurrent, infected, or ingrown nails with severe inflammation or in failure of conservative measures
    • Partial nail avulsion or complete nail excision
    • Antibiotics are not recommended unless cellulitis occurs.