Differentials
Necrotizing fasciitis
SIGNS / SYMPTOMS
Initial findings are nonspecific and can be similar to those of cellulitis.
Marked pain, often out of proportion to the exam, and necrotic bullous change are clinical clues.
Crepitus may be present as a late finding if a mixed anaerobic etiology is responsible.
INVESTIGATIONS
Surgical exploration is definitive for diagnosis and a requirement for treatment. This is limb- and potentially life-threatening, and surgical consultation should not be delayed if necrotizing fasciitis is suspected. MRI is helpful if the diagnosis is in doubt.[47][48]
MRI: contrast enhancement, thickening of deep fasciae with fluid collection.
Thrombophlebitis, superficial
SIGNS / SYMPTOMS
Tender, palpable cord along affected vein often present.
Presence or recent presence of intravenous catheter or needle also suggests this diagnosis.
INVESTIGATIONS
Clinical diagnosis.
Deep vein thrombosis
SIGNS / SYMPTOMS
Tenderness of involved vein, history of prior deep vein thrombosis, prolonged immobility, or hypercoagulable state.
INVESTIGATIONS
Duplex ultrasonography: presence of a thrombus within the vein.
Gout
SIGNS / SYMPTOMS
Suspected in those with history of gout or if area of skin involvement is closely associated with a joint, particularly the first metatarsophalangeal or knee joint.
INVESTIGATIONS
Presence of urate crystals in joint aspirate.
Lyme disease
SIGNS / SYMPTOMS
Also known as erythema migrans.
Residence in or travel to endemic area, history of tick exposure, involvement of sites that are unusual for bacterial cellulitis (e.g., axilla, popliteal fossa, or abdomen) are suggestive.[49]
Sometimes has an area of central clearing within the erythema.
Dermatitis, contact
SIGNS / SYMPTOMS
Well-demarcated skin involvement, pruritus, and exposure history are suggestive.[52]
Often diagnosed on clinical grounds alone.
INVESTIGATIONS
Biopsy: intraepidermal spongiosis with monocyte and histiocyte dermal infiltration suggest an allergic contact dermatitis. Irritant dermatitis is characterized by superficial vesicles containing polymorphonuclear leukocytes.[53]
Insect bites and stings
SIGNS / SYMPTOMS
History of insect exposure and pruritus. Often diagnosed on clinical grounds alone.
INVESTIGATIONS
Biopsy: wedge-shaped dermal mixed inflammatory infiltrate is characteristic. Eosinophils often predominate.[53]
Fixed drug reactions
SIGNS / SYMPTOMS
History of similar reaction with prior exposure to same drug; well-demarcated round or oval area of involvement; itching, burning; involvement of lips and/or genitalia.
INVESTIGATIONS
Clinical diagnosis.
Eosinophilic cellulitis (Wells syndrome)
SIGNS / SYMPTOMS
A short prodrome of itching and burning may precede onset of single or multiple lesions. Recurrence is common and resolution of each episode may occur over weeks.[54]
INVESTIGATIONS
Histopathology: dermal infiltration with eosinophils and a peripheral eosinophilia can be seen as well.[54]
Sweet syndrome
Inflammatory carcinoma (carcinoma erysipeloides)
SIGNS / SYMPTOMS
Involvement of breast, absence of fever.
This represents an advanced form of cancer.
INVESTIGATIONS
Mammography and biopsy should not be delayed.
Relapsing polychondritis
SIGNS / SYMPTOMS
Bilateral involvement, particularly of auricular (pinnae spared) or nasal cartilage, history of similar reaction.[56]
INVESTIGATIONS
Clinical diagnosis.
Calciphylaxis
SIGNS / SYMPTOMS
Painful, retiform lesions, often below the knee, with palpable characteristic subcutaneous plaques. Subsequent ulceration may develop. Seen most often in patients with end stage renal disease.[57]
INVESTIGATIONS
Diagnosis is often made clinically, especially with evolution of lesions. Biopsy is generally avoided due to concern over poor subsequent healing.[57]
Lipodermatosclerosis
Familial Mediterranean fever
SIGNS / SYMPTOMS
A positive family history, recurrent episodes, association with syndrome of fever, serositis, and lower extremity involvement with erysipelas-like lesions are suggestive.[52]
INVESTIGATIONS
Clinical diagnosis.
Lymphedema
SIGNS / SYMPTOMS
History of malignancy, previous surgery, radiation therapy, travel to endemic filariasis area, or family history of lymphedema. Painless unilateral swelling of extremity; non-pitting edema; skin changes. Symptoms of limb heaviness or weakness.
INVESTIGATIONS
Lymphoscintigram: dermal backflow, delayed or absent transport, or lack of visualization of lymph nodes.
MRI or CT scan of affected extremity: thickened skin; honeycombing of fluid and fibrous tissue above the muscle fascia.
Ultrasound of affected area: thickening of epifascial compartment and skin.
Lymphangiography: location of a specific anatomic obstruction.
Blood smear for filariasis: presence of microfilariae.
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