Differential Diagnosis for Thumbnail with Foul Odor and Fungal Infection

• Single Most Likely Diagnosis
  • Onychomycosis: This is the most common fungal infection of the nails, characterized by a foul odor, thickening, and discoloration of the nail. The presence of a fungal infection and foul odor strongly points towards onychomycosis.
• Other Likely Diagnoses
  • Paronychia: An infection of the skin around the nail, which can be caused by bacteria or fungi. It often presents with redness, swelling, and sometimes a foul odor, especially if there is a secondary bacterial infection.
  • Onychocryptosis (Ingrown Nail): While more commonly associated with pain and inflammation, an ingrown nail can also lead to a foul odor if there is a secondary infection.
• Do Not Miss Diagnoses
  • Diabetic Foot Infection: Although less common in the thumbnail, individuals with diabetes are prone to foot infections, which can spread and have serious consequences if not promptly treated. A foul odor can be a sign of a more serious underlying infection.
  • Cellulitis: A bacterial skin infection that can spread rapidly and is a medical emergency. While less likely to be confined to the thumbnail, it's crucial not to miss this diagnosis due to its potential severity.
• Rare Diagnoses
  • Chromoblastomycosis: A rare fungal infection of the skin and subcutaneous tissue that can involve the nails and is characterized by the presence of specific fungal forms (sclerotic bodies) in the tissue.
  • Sporotrichosis: A fungal infection caused by Sporothrix schenckii, which can affect the skin and nails, often acquired through cutaneous inoculation. It's rare but can present with a variety of skin and nail manifestations, including a foul odor.