What type of peripheral neuropathy does diabetes primarily cause?

Diabetic Peripheral Neuropathy: Types and Characteristics

Diabetes primarily causes distal symmetric polyneuropathy (DSPN), which affects both small and large nerve fibers and presents with a characteristic "glove and stocking" distribution pattern. 1, 2

Types of Diabetic Neuropathy

Distal Symmetric Polyneuropathy (DSPN)

• Most common form of diabetic neuropathy (affects up to 50% of patients with long-duration diabetes) 1, 3
• Characterized by:
  • Bilateral and symmetrical distribution
  • Distal-to-proximal progression (starts in toes/feet, progresses upward)
  • Sensory symptoms predominate over motor symptoms
  • Affects both small and large nerve fibers 1

Small Fiber Involvement

• Early manifestations include:
  • Pain and dysesthesia (burning, tingling sensations)
  • Temperature sensation impairment
  • Pinprick sensation abnormalities 1
• Small fiber damage often precedes large fiber damage 1
• Assessment: Temperature and pinprick sensation testing 1

Large Fiber Involvement

• Later manifestations include:
  • Numbness
  • Loss of protective sensation (LOPS)
  • Vibration perception deficits
  • Diminished ankle reflexes 1
• Assessment: Vibration testing with 128-Hz tuning fork, 10-g monofilament testing, ankle reflex testing 1

Autonomic Neuropathy

• Often coexists with DSPN
• Manifestations include:
  • Cardiovascular: Resting tachycardia, orthostatic hypotension 1
  • Gastrointestinal: Gastroparesis, constipation, diarrhea 1
  • Genitourinary: Sexual dysfunction, bladder dysfunction 1
  • Sudomotor: Dry, cracked skin in extremities 1

Clinical Significance and Complications

• Up to 50% of diabetic peripheral neuropathy may be asymptomatic 1
• Loss of protective sensation increases risk for:
  • Foot injuries
  • Diabetic foot ulcers
  • Amputations 1, 3
• Painful neuropathy significantly impacts quality of life 2

Pathophysiology

• Primary mechanisms:
  • Hyperglycemia (primary driver in type 1 diabetes) 2
  • Dyslipidemia (primary driver in type 2 diabetes) 2
  • Oxidative stress
  • Microvascular damage
  • Neuroinflammation 4, 5
• Advanced glycation end products (AGEs) trigger inflammatory pathways 5

Diagnosis and Assessment

• Diagnosis of exclusion (rule out other causes of neuropathy) 1, 3
• Recommended testing:
  1. Small-fiber function: Pinprick and temperature sensation
  2. Large-fiber function: Vibration perception (128-Hz tuning fork), 10-g monofilament, ankle reflexes
  3. Protective sensation: 10-g monofilament 1
• Screening timeline:
  • Type 1 diabetes: Begin 5 years after diagnosis
  • Type 2 diabetes: Begin at diagnosis
  • All patients: Annual assessment thereafter 1

Treatment Approach

• Glycemic control:
  • Prevents DPN in type 1 diabetes
  • Modestly slows progression in type 2 diabetes
  • Does not reverse neuronal loss 1
• Pain management for symptomatic neuropathy:
  • First-line medications: Pregabalin, duloxetine, or gabapentin 1, 3
  • Second-line options: Tricyclic antidepressants, SNRIs, opioids 3, 2
• Foot care education and regular foot examinations are essential for preventing complications 3

Clinical Pearls

• Diabetic neuropathy is a diagnosis of exclusion - consider other causes of neuropathy in diabetic patients 1
• Electrophysiological testing or neurology referral is rarely needed unless clinical features are atypical 1
• The greatest risk from small-fiber neuropathy is foot ulceration leading to gangrene and amputation 6
• Regular comprehensive foot examinations are critical for early detection of complications 3