SN2 SHORT NOTE 5M

Define Cellulitis. Describe its clinical features and management.

General Surgery · Final Professional

What It Is

Cellulitis is a spreading, non-suppurative infection of the subcutaneous and connective tissue, usually caused by Streptococcus pyogenes (and sometimes Staphylococcus aureus). The word to hold onto is spreading — and understanding why it spreads rather than localises is the key to the whole topic.

CLINICAL PEARL

Clinical pearl: The contrast with an abscess comes down to the organism's enzymes. Streptococcus pyogenes produces 'spreading factors' — streptokinase, hyaluronidase and streptodornase — that dissolve fibrin and break down the tissue's ground substance, so the infection diffuses freely through the tissue planes and never walls itself off. Staphylococcus aureus, by contrast, produces coagulase, which clots the surrounding plasma and walls the infection off into a localised abscess. That single difference explains why cellulitis is diffuse with no pus to drain, whereas a staphylococcal infection forms a discrete collection.

Clinical Features — and WHY

Diffuse, spreading erythema with warmth, swelling and tenderness, and characteristically ill-defined margins — because there is no wall containing it (unlike the sharply localised abscess).
Fever, and often lymphangitis (red streaks tracking to the regional nodes) and tender lymphadenopathy, as the infection travels along lymphatics.
A portal of entry — a crack, ulcer, tinea between the toes or insect bite — can often be found, and predisposing factors include diabetes, lymphoedema and venous insufficiency.

Management

Because cellulitis is a diffuse infection of well-perfused living tissue with no avascular pus pocket, it responds to antibiotics (anti-streptococcal/anti-staphylococcal) — the exact opposite of an abscess, which needs drainage. Add rest and elevation of the part to reduce oedema, analgesia, and treatment of the portal of entry and underlying factors. It is wise to mark the margin of erythema so progression or response can be judged, and to watch for the development of an abscess or, more dangerously, necrotising fasciitis — signalled by pain out of proportion, dusky skin, bullae or crepitus.

Absence of a drainable collection distinguishes it from abscess.

KEY POINT

Key points TO remember

Spreading, non-suppurative subcutaneous infection; usually Streptococcus pyogenes.
Spreads because Strep makes streptokinase/hyaluronidase (dissolve barriers); Staph coagulase walls off → abscess instead.
Diffuse erythema with ill-defined margins, warmth, fever, lymphangitis; find the portal of entry.
Treat with antibiotics + rest + elevation (no pus to drain); watch for abscess or necrotising fasciitis.

EXAM TIP

Sources: Bailey & Love's Short Practice of Surgery.

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