What labs and imaging studies should be ordered for a patient presenting with red and purple discoloration of the feet, intermittent cold and hot sensations, and vision changes?

Diagnostic Workup for Red/Purple Feet with Temperature Changes and Vision Changes

For a patient presenting with red and purple discoloration of the feet, intermittent cold and hot sensations, and vision changes, a comprehensive vascular and neurological evaluation is essential, including duplex ultrasound, ankle-brachial index, and MRI of the brain. 1

Initial Laboratory Tests

• Complete Blood Count (CBC): To assess for infection, inflammation, or hematologic disorders
• Comprehensive Metabolic Panel: To evaluate kidney and liver function
• Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP): To detect inflammatory processes 1
• Hemoglobin A1c: To screen for diabetes, which can cause both peripheral vascular disease and vision changes 1
• Lipid Panel: To assess cardiovascular risk factors
• Coagulation Studies (PT/INR, PTT): To evaluate for hypercoagulable states
• Autoimmune Panel: Including ANA, ANCA, rheumatoid factor, and complement levels to assess for vasculitis

Vascular Assessment

• Ankle-Brachial Index (ABI): Essential first-line test to evaluate peripheral arterial disease 1
• Handheld Doppler Assessment: For rapid confirmation of arterial occlusion 1
• Duplex Ultrasound: To evaluate arterial and venous circulation in the lower extremities 1
• Skin Temperature Measurement: Using infrared thermometry with standardized approach, comparing affected limb to contralateral side 1

Advanced Imaging

• MRI of Brain and Orbits: To evaluate for central causes of vision changes and to rule out cerebrovascular events 2
• CT Angiography (CTA) or MR Angiography (MRA) of lower extremities: For detailed vascular assessment if ABI/duplex ultrasound suggests vascular compromise 1
• Digital Subtraction Angiography (DSA): Gold standard for diagnosing acute limb ischemia if immediate intervention may be needed 1

Specialized Tests

• Ophthalmologic Examination: Including fundoscopy to evaluate retinal vasculature and visual acuity testing
• Echocardiography: If cardiac embolism is suspected as a source of peripheral vascular symptoms 1
• Skin Biopsy: If vasculitis or other dermatologic conditions are suspected based on the pattern of discoloration 3

Diagnostic Algorithm

1. Initial Assessment:

   • Perform ABI and handheld Doppler assessment immediately
   • Order basic labs (CBC, CMP, ESR, CRP, HbA1c)
   • Measure skin temperature difference between affected and unaffected limbs

2. If ABI is abnormal (<0.9):

   • Proceed with duplex ultrasound
   • Consider CTA or MRA based on severity
   • If severe ischemia is suspected, proceed directly to DSA for potential intervention

3. If ABI is normal but symptoms persist:

   • Complete autoimmune workup
   • Consider skin biopsy
   • Evaluate for neurological causes with MRI brain/orbits

4. For vision changes:

   • Urgent ophthalmologic consultation
   • MRI of brain and orbits
   • Consider carotid imaging if retinal ischemia is suspected

Important Considerations

• The combination of peripheral vascular symptoms with vision changes suggests potential systemic vascular disease or embolic phenomena 1
• Temperature changes in the feet may indicate peripheral neuropathy, especially in diabetic patients 4
• Red/purple discoloration may represent exercise-induced purpura, vasculitis, or medication side effects 3, 5
• Vision changes concurrent with vascular symptoms warrant urgent neurological and ophthalmological evaluation to rule out cerebrovascular events

Pitfalls to Avoid

• Attributing symptoms solely to peripheral vascular disease without investigating central causes
• Failing to perform temperature comparison between affected and unaffected limbs
• Relying only on duplex ultrasound in cases of suspected multilevel disease, as its accuracy may be limited 1
• Delaying advanced imaging in patients with both peripheral vascular and vision symptoms, as this combination may indicate systemic vascular disease requiring prompt intervention

The diagnostic approach should be expedited, particularly when both vascular symptoms and vision changes are present, as this combination may indicate serious systemic disease requiring urgent intervention.