Workup for Lower Extremity Numbness in an 86-Year-Old Patient
The appropriate workup for an 86-year-old patient with lower extremity numbness should begin with a thorough vascular assessment including ankle-brachial index (ABI) measurement, followed by neurological evaluation to differentiate between peripheral arterial disease and neuropathic causes.
Initial Assessment
Vascular Evaluation
- Perform comprehensive pulse examination with numerical grading (0-3) of all lower extremity pulses (femoral, popliteal, dorsalis pedis, posterior tibial) 1
- Measure blood pressure in both arms to identify potential subclavian stenosis (difference >15-20 mmHg is abnormal) 2
- Auscultate for femoral bruits 1
- Inspect legs and feet for:
- Color and temperature changes
- Hair loss or trophic changes
- Skin integrity and presence of ulcerations
- Distribution of edema (if present) 1
Ankle-Brachial Index (ABI)
- Measure ABI as first-line diagnostic test for peripheral arterial disease (PAD) 2
- ABI interpretation:
- Normal: 1.0-1.4
- Borderline: 0.91-0.99
- Mild-moderate PAD: 0.41-0.90
- Severe PAD: ≤0.40 1
- If resting ABI is normal but symptoms persist, perform exercise ABI testing 2
- For non-compressible vessels (ABI >1.40), use toe-brachial index instead 2
Neurological Evaluation
- Assess sensory function:
- Light touch sensation
- Proprioception
- Temperature and pinprick sensation
- Distribution pattern (stocking-glove vs dermatomal) 3
- Test deep tendon reflexes
- Evaluate for muscle weakness and atrophy
- Assess gait and balance 4
Laboratory Testing
Initial Laboratory Panel
- Complete blood count
- Comprehensive metabolic panel
- Fasting blood glucose or HbA1c
- Vitamin B12 level
- Thyroid-stimulating hormone
- Serum protein electrophoresis with immunofixation 3
Additional Testing Based on Clinical Suspicion
- Lipid panel if cardiovascular risk factors present 1
- Creatine kinase if myopathy suspected 1
- HbA1c if diabetes suspected but not previously diagnosed
- Consider testing for less common causes if initial workup is negative:
- Heavy metal screening
- Lyme disease serology
- HIV testing
- Vasculitis markers (ESR, CRP, ANCA)
Advanced Diagnostic Testing
Electrodiagnostic Studies
- Nerve conduction studies and electromyography to:
- Differentiate axonal vs demyelinating neuropathy
- Determine distribution (length-dependent vs non-length-dependent)
- Assess severity 3
Vascular Imaging
- Duplex ultrasound if PAD is suspected based on ABI 2, 1
- Consider CT angiography or MR angiography if:
- Revascularization is being considered
- Duplex ultrasound is inconclusive 1
Advanced Neuroimaging
- MRI of lumbosacral spine if radiculopathy is suspected
- MRI of brain if central causes are suspected (especially with concurrent symptoms like vertigo or cognitive changes) 5
Common Pitfalls and Caveats
Avoid attributing symptoms solely to age - Lower extremity numbness is not a normal part of aging and requires thorough evaluation
Don't miss concurrent conditions - Peripheral neuropathy and PAD commonly coexist, particularly in patients with diabetes 1
Consider medication-induced neuropathy - Review medication list for potential neurotoxic agents (e.g., chemotherapeutics, certain antibiotics) 6
Remember fall risk - Patients with peripheral neuropathy have increased risk of falls and fractures; assess and address this risk 4
Don't overlook central causes - While peripheral causes are common, central nervous system pathology can present with similar symptoms 5, 7
Recognize that "asymptomatic" PAD may present with subtle functional impairment - Patients may have adapted to gradual functional decline 2
By following this systematic approach, you can effectively evaluate the cause of lower extremity numbness in an elderly patient and develop an appropriate management plan based on the underlying etiology.