Differential Diagnosis for Cellulitis

Single Most Likely Diagnosis

• Bacterial Cellulitis: This is the most common cause of cellulitis, typically caused by Streptococcus or Staphylococcus species. The presentation of redness, warmth, swelling, and tenderness in a localized area is classic for bacterial cellulitis.

Other Likely Diagnoses

• Eczema/Dermatitis: Can present with similar symptoms to cellulitis, such as redness and swelling, but is typically more pruritic and has a different distribution.
• Contact Dermatitis: An allergic or irritant reaction to a substance that comes into contact with the skin, which can mimic cellulitis.
• Insect Bites: Can cause localized reactions that resemble cellulitis, especially if there is a significant allergic response.

Do Not Miss Diagnoses

• Necrotizing Fasciitis: A life-threatening condition that presents with severe pain, swelling, and redness, but also signs of necrosis such as blisters, bullae, or skin sloughing. Early recognition is crucial.
• Gas Gangrene: Caused by Clostridium species, it presents with severe pain, swelling, and crepitus (gas in the tissues), which can be mistaken for cellulitis but requires immediate surgical intervention.
• Deep Vein Thrombosis (DVT): Can present with swelling and redness of the leg, similar to cellulitis, but typically has a more pronounced swelling and pain with palpation of the deep veins.

Rare Diagnoses

• Erysipelas: A type of cellulitis that is more superficial and demarcated, typically caused by Streptococcus species.
• Mycobacterial Infections: Such as Mycobacterium marinum, which can cause skin infections that resemble cellulitis, especially in individuals who work with fish or aquariums.
• Fungal Infections: Like sporotrichosis, which can cause a chronic, nodular lesion that can be mistaken for cellulitis, especially in gardeners or those who work with plants.