Cellulitis

Question 1

Pathology, signs and symptoms

Answer 1

Cellulitis is an acute bacterial infection of the skin and subcutaneous tissues. It primarily affects the deeper layers of the skin, including the dermis and subcutaneous fat. The pathology of cellulitis involves the following key aspects:

• Most common pathogens:
  
  • Staphylococcus aureus (including MRSA)
  • Streptococcus pyogenes (Group A Streptococcus)
• Less commonly, other bacteria such as Haemophilus influenzae or Pseudomonas can be involved, especially in certain environments or in immunocompromised patients.

• Entry of bacteria: Cellulitis typically occurs when bacteria enter through a break in the skin, such as a cut, scrape, insect bite, or surgical wound. Skin conditions like eczema or athlete’s foot, which compromise the skin barrier, can also predispose to cellulitis.
• Infection spread: Once the bacteria enter the skin, they multiply and release enzymes and toxins that break down tissue. The infection spreads within the dermis and subcutaneous tissues.
• Inflammatory response: The body’s immune system reacts to the bacterial invasion by releasing inflammatory mediators (cytokines), leading to redness, warmth, swelling, and pain in the affected area.

• Erythema: Redness of the skin caused by inflammation.
• Edema: Swelling due to fluid accumulation in tissues.
• Pain: Localized tenderness over the affected area.
• Fever and malaise: Systemic symptoms can occur if the infection spreads.
• Skin changes: The affected area may become tight and glossy due to the swelling, and in severe cases, blisters or abscesses can form.

• Lymphangitis: The infection can spread to the lymphatic system.
• Sepsis: If left untreated, the infection can enter the bloodstream, leading to sepsis, a life-threatening condition.
• Necrotizing fasciitis: In rare, severe cases, cellulitis may progress to deeper tissues, causing necrosis (tissue death).

• Skin trauma: Cuts, burns, or surgical wounds.
• Weakened immune system: Due to conditions like diabetes, HIV, or immunosuppressive drugs.
• Chronic swelling: Lymphedema or venous insufficiency increases susceptibility to cellulitis.

• On histological examination, cellulitis shows diffuse neutrophilic infiltration of the dermis and subcutaneous tissues.
• There may be dermal edema and dilation of lymphatic vessels due to the inflammatory response.

• Antibiotics: Empiric treatment typically involves antibiotics targeting Staphylococcus and Streptococcus species. In more severe cases, intravenous antibiotics may be required.
• Supportive care: Elevating the affected limb and managing symptoms with analgesics.

Understanding the pathology of cellulitis is essential for effective diagnosis and treatment, especially to prevent complications such as sepsis or tissue necrosis.