What tests are used to diagnose diabetic neuropathy?

Diagnostic Tests for Diabetic Neuropathy

For diagnosing diabetic neuropathy, a comprehensive neurological evaluation should include temperature sensation, pinprick sensation, vibration perception, pressure sensation, and ankle reflexes testing. 1

Timing of Screening

• Type 1 diabetes: Begin screening 5 years after diagnosis, then annually
• Type 2 diabetes: Begin screening at time of diagnosis, then annually 1

Primary Diagnostic Tests

1. Small-Fiber Function Assessment

• Temperature sensation: Assess ability to distinguish between warm and cold stimuli
• Pinprick sensation: Test ability to feel sharp sensation 1

2. Large-Fiber Function Assessment

• Vibration perception: Use 128-Hz tuning fork on bony prominences (great toe, medial malleolus)
• Lower-extremity reflexes: Test ankle reflexes
• 10-g monofilament testing: Apply to standardized sites on feet 1

3. Protective Sensation Assessment

• 10-g monofilament testing: Critical for identifying feet at risk for ulceration and amputation 1

Diagnostic Algorithm

1. Initial screening: Apply temperature/pinprick sensation (small-fiber) AND vibration sensation/10-g monofilament (large-fiber) tests
2. Interpretation:
   • Abnormal findings in ≥2 tests strongly suggest diabetic neuropathy
   • Positive test is typically represented by ≥5 incorrect responses out of 8 stimuli applied 2
3. Confirmatory testing: If clinical findings are equivocal or atypical, proceed to neuroelectrophysiological examination (electromyography) 1

Autonomic Neuropathy Screening

If peripheral neuropathy is detected or if patient has other microvascular complications, screen for autonomic neuropathy:

1. Cardiac autonomic neuropathy: Heart rate variability testing, postural hypotension testing, ambulatory blood pressure monitoring
2. Gastrointestinal neuropathy: Scintigraphy, electrogastrography
3. Urogenital dysfunction: Bladder ultrasound (volume and residual urine) 1

Clinical Pearls and Pitfalls

• Important caveat: Diabetic neuropathy is a diagnosis of exclusion. Always rule out other causes of neuropathy that may be treatable 1
• Common pitfall: Up to 50% of diabetic peripheral neuropathy cases are asymptomatic, making screening essential even in absence of symptoms 1
• Efficiency tip: The 10-g SWME, superficial pain test, and vibration testing by the on-off method each require only about 60 seconds to administer 2
• Advanced testing: For research purposes or atypical presentations, skin biopsy for intra-epidermal nerve fiber density and confocal corneal microscopy may detect early neuropathy 3

Remember that early detection of diabetic neuropathy is crucial as it allows for interventions that can reduce morbidity and mortality through prevention of foot ulcers, amputations, and other complications that significantly impact quality of life.