Finger and toe infections

Finger and toe infections are common conditions with a variety of causes, frequently manifesting with classic signs of inflammation. The most common types of finger infections are paronychia, felon, and herpetic whitlow; an ingrown toenail is the most common cause of toe infection. All of these conditions are clinical diagnoses. Treatment depends on the type and severity of the infection, but should not be delayed to prevent potentially severe complications, such as cellulitis, osteomyelitis, and soft tissue necrosis. Paronychias are acute or chronic inflammations of the nail folds, most commonly of the fingernails. Acute paronychia is typically caused by bacterial infection following trauma to the nail folds. The cause of chronic paronychia is multifactorial, although continuous exposure to moisture and/or skin irritants (e.g., dishwashing soap) often plays a role. Acute paronychia is frequently treated with topical antibiotics, while chronic paronychia is treated with topical steroids and avoidance of stressors. Felons are subcutaneous infections of the finger pulp, most commonly caused by bacterial infection secondary to minor trauma or progression of untreated acute paronychia. Early stages can be managed conservatively with analgesics and oral antibiotics; later stages, characterized by abscess formation, require incision and drainage. Herpetic whitlows are infections of the fingers caused by herpes simplex virus that typically manifest with nonpurulent vesicles and signs of inflammation over the pulp of the distal phalanx (see “Herpes simplex virus infections” for a more detailed discussion). An ingrown toenail is the abnormal growth of a nail plate into the lateral periungual skin of the nail fold. This condition most commonly affects the big toe and is often associated with improper trimming of the toenail. The disruption of the cutaneous barrier by the ingrown toenail results in an inflammatory foreign body reaction with the risk of subsequent infection. While conservative management involving the placement of cushioning material (e.g., cotton) under the ingrown nail plate may be sufficient in early stages, partial nail avulsion or complete nail excision is necessary eventually.

Paronychia ^[1][2]

Felon (pulp space infection) ^[3][4]

• Definition: subcutaneous infection of the distal pulp of the finger
• Etiology
  • Trauma (e.g., minor cuts, splinters)
  • Progression of untreated paronychia
  • Pathogen: Staphylococcus aureus (most common)
• Clinical features: commonly involves the thumb and index finger
  • Classic signs of inflammation with tense swelling confined to the distal digital pulp
  • Fluctuance and spontaneous drainage
• Diagnostics: clinical diagnosis
• Treatment
  • Without abscess formation: warm soaks, elevation, and oral β-lactamase resistant antibiotics (e.g., cephalexin or oxacillin)
  • With abscess formation: surgical drainage
  • Tetanus prophylaxis
• Complications: septic arthritis, osteomyelitis, and soft tissue necrosis

Blistering distal dactylitis ^[5][6]

• 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)

Herpetic whitlow ^[3]

• 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 “Herpes simplex virus infections.”

Ingrown toenail ^[7][8]

• 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 ^[9]
  • 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.