Differentials
Staphylococcal skin lesions
Erysipelas
SIGNS / SYMPTOMS
History of recent pharyngitis. Infants and older people are usually affected. Pruritus and burning are present before the dermatosis.[1] Sharply delineated, painful lesion with a bright red, oedematous, indurated (peau d'orange) appearance. Bullae only in 5% of cases.
INVESTIGATIONS
Antistreptococcal antibodies may be detectable.
Cellulitis
SIGNS / SYMPTOMS
Absence of purple or red bullous lesions, absence of crepitus, intact sensation distal to the affected area, and comparatively slow spread. Systemic toxicity (e.g., renal failure, hypotension, and acidosis) usually absent with cellulitis.
INVESTIGATIONS
Serous discharge may be expressed on compression of the wound margins, and streptococci can be identified on a Gram-stained smear.[1]
Imaging studies (radiography, CT, and MRI): absence of the gas, fascial enhancement, and soft-tissue oedema characteristic of gangrene.
Insect bites
SIGNS / SYMPTOMS
History of insect or spider bite, or suitable clinical scenario. The bite of the brown recluse spider (Loxosceles reclusa) can produce a necrotising skin lesion that resembles infectious gangrenous cellulitis. Fever is not commonly present, but the occurrence of fever and chills 24 to 48 hours after the bite enhances the mimicry.[1]
INVESTIGATIONS
Clinical diagnosis.
Deep vein thrombosis (DVT)
SIGNS / SYMPTOMS
Formation of a blood clot in a deep vein, most commonly in the legs or pelvis. Symptoms can include pain, swelling, redness, and enlarged veins in the affected area, but some DVTs have no symptoms.
INVESTIGATIONS
Doppler ultrasound detects changes of blood flow; absence of blood flow indicates DVT.
Pyomyositis
SIGNS / SYMPTOMS
Bacterial infection of the skeletal muscles that results in an abscess. Causes pain and tenderness of the affected muscle, and fever, followed by abscess formation.
INVESTIGATIONS
CT and/or MRI. Abscess appears as fluid collection with peripheral rim enhancement.
Pyoderma gangrenosum
SIGNS / SYMPTOMS
Rare, inflammatory skin disease, in which painful pustules or nodules become ulcers that progressively grow.
INVESTIGATIONS
Clinical diagnosis and/or CT, MRI, or biopsy. Skin biopsy excludes other conditions.
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