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Signature ✍️
- “Red leg” is an extremely broad term that refers to the finding of leg erythema due to both infectious & non-infectious etiologies
- There are a few different lenses through which “red leg” can be analyzed, which should really be run “in parallel” rather than “in sequence”
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DDx (Lenses) 🏳️🌈
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- Unilateral (Infectious ≈ Non-Infectious) 🦵
- Skin & soft tissue infection (SSTI, i.e. cellulitis & erysipelas)
- Deep vein thrombosis (DVT)
- Septic arthritis, bursitis, osteomyelitis (OM)
- (Pseudo)gout
- Neurogenic osteoarthropathies
- Zoster
- Bilateral (Non-Infectious > Infectious) 🦵🦵
- Chronic venous stasis +/- Acute stasis dermatitis
- Lymphedema
- Lipodermatosclerosis
- Panniculitis DDx
- Vasculitis DDx
⚪ The finding of bilateral superficial fungal infection (i.e. tinea corporis) is the exception to the rule for bilateral “red leg”
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- Acute: DDx mirrors that of unilateral disease (i.e. infectious ≈ non-infectious), with addition of inflammatory systemic diseases (e.g. vasculitis, panniculitis)
- Chronic: DDx mirrors that of bilateral disease (i.e. non-infectious > infectious), with subtraction of inflammatory systemic diseases (e.g. vasculitis, panniculitis)
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- Local 👉
- Uncomplicated SSTI
- (Pseudo)gout (Exception = polyarticular gout)
- IV infiltration & Fixed drug eruption
- Dermatitis (e.g. acute stasis, irritant)
- Neurogenic osteoarthropathies
- Systemic 🚹
- SIRS
- Complicated SSTI, Erysipelas, Staph. scalded skin syndrome
- Deeper infections (e.g. abscess, nec. fasc., OM)**
- Septic arthritis & bursitis**
- Dyspnea
- DVT → Pulmonary embolism
- Decompensated CHF
- Whole Body Rash
- Separate DDx***
***Can’t miss = microvascular occlusion syndromes (i.e. retiform purpua → necrosis) & SJS/TEN
**Septic arthritis, bursitis, & OM need not be accompanied by SIRS findings
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- Rapid Improvement (Arteriolar Vasodilation) 💥
- Peripheral artery disease (PAD)
- Neurogenic osteoarthropathies (i.e. acute Charcot, CRPS)
- Slow Improvement (Venous Hypertension) ⏳
- Decompensated CHF
- Deep vein thrombosis
- ⊖ Change (Capillary Leak) 🚫
- Skin & soft tissue infections
- Dermatitis (e.g. acute stasis, irritant)
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Principles❗️
Diagnosis of Cellulitis 🔥
- The “ALT-70 Score” may be helpful in determining when to consult Infectious Diseases in trickier cases:
Scoring
- Asymmetry (+3)
- Leukocytosis (+1)
- Tachycardia (+1)
- Age > 70 (+2)
Interpretation
- Score < 2 → unlikely to be cellulitis (83% specificity)
- Score 2 - 5 → consider ID consultation
- Score > 5 → treat for cellulitis (82% specificity)
“It’s Never Bilateral Cellulitis” ❌
- While chronic, bilateral conditions are almost universally non-infectious, these conditions do increase the risk of developing acute, overlying fungal infection (i.e. tinea corporis) as well as cellulitis. These are tricky cases, particularly when the baseline findings are unknown
- Key features that suggest non-infectious culprits of “red leg” include bilateral involvement, chronic tempo, & ⊖ pain; the converse findings (i.e. unilateral involvement, acute tempo, & ⊕ pain) more commonly represent some form of infection, but by no means in all cases
The “Red Leg” Raise 👆
Principle #1
- Leaky blood vessels will remain leaky no matter the position of the leg. Therefore, findings related to dermatitis & SSTI should not change upon leg elevation
Principle #2
- Arterioles of the legs/feet can be vasodilated as a response to 3 groups of diseases, which lead to the observation of “red” leg due to flushing associated w/ vasodilatation
- The 3 groups are peripheral artery disease (compensation for poor large artery flow), neurogenic osteoarthropathy (pathologic vasodilation due to dysregulated nerve-vessel cross-talk), & venous hypertension (compensation for poor large vein flow)
- This vasodilatation can be overcome when raising the leg due to gravity’s effects on arteriolar blood volume drainage
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