What is Diabetic Neuropathy

Diabetic neuropathy is nerve damage caused by diabetes mellitus, representing the most common cause of peripheral neuropathy in developed countries.

What is involved?

Multiple nerve types can be affected:

• Peripheral sensory nerves (most common)
• Peripheral motor nerves
• Autonomic nerves
• Individual nerves (mononeuropathy)
• Multiple individual nerves (mononeuropathy multiplex)

Types of Diabetic Neuropathy

1. Distal Symmetric Polyneuropathy (DSPN) - most common (75%)
2. Diabetic Amyotrophy (Proximal Diabetic Neuropathy)
3. Autonomic Neuropathy
4. Mononeuropathies (cranial nerves, carpal tunnel, etc.)
5. Small Fiber Neuropathy

Location

• DSPN: length-dependent, starts in feet and progresses proximally
• Diabetic Amyotrophy: proximal legs (thighs), often asymmetric
• Mononeuropathies: focal nerve involvement (median, ulnar, peroneal, cranial nerves III, VI, VII)

Common symptoms

Distal Symmetric Polyneuropathy

• Numbness, tingling in feet (later hands)
• Burning, electric shock-like pain
• “Stocking-glove” distribution
• Worse at night
• Loss of balance, unsteady gait
• Foot ulcers (due to loss of protective sensation)

Diabetic Amyotrophy

• Severe thigh pain (often unilateral initially)
• Proximal leg weakness
• Weight loss
• Can be the presenting symptom of diabetes

Autonomic Neuropathy

• Orthostatic hypotension
• Gastroparesis
• Constipation, diarrhea
• Bladder dysfunction
• Erectile dysfunction
• Abnormal sweating

Small Fiber Neuropathy

• Burning pain
• Allodynia (pain from light touch)
• Normal strength and reflexes
• May have normal standard nerve conductions

Onset

• DSPN: gradual over years
• Diabetic amyotrophy: subacute over weeks to months
• Mononeuropathies: acute to subacute

Risk factors

• Duration of diabetes (most important)
• Poor glycemic control (elevated HbA1c)
• Type 1 > Type 2 for some complications
• Hypertension
• Dyslipidemia
• Obesity
• Smoking
• Alcohol use
• Chronic kidney disease
• Height (longer nerves more vulnerable)

Exam

Distal Symmetric Polyneuropathy

• Decreased sensation in stocking-glove pattern
• Reduced vibration sense (test with 128 Hz tuning fork)
• Reduced proprioception
• Decreased or absent ankle reflexes
• May have decreased knee reflexes in severe cases
• Distal muscle weakness and atrophy (late finding)
• Foot deformities, calluses, ulcers

Diabetic Amyotrophy

• Proximal leg weakness (quadriceps, hip flexors)
• Thigh muscle atrophy
• Knee reflex may be reduced or absent
• Sensory loss less prominent

Screening Tests

• 10-gram monofilament testing
• Vibration with 128 Hz tuning fork
• Ankle reflexes
• Pin prick sensation

EMG

EMG and nerve conduction studies are essential for diagnosis and classification.

DSPN Findings

• Sensory nerve studies: reduced amplitudes (sural most sensitive), prolonged latencies, slowed velocities
• Motor nerve studies: reduced amplitudes, slowed velocities
• Length-dependent pattern (lower extremity worse than upper)
• Axonal pattern predominates (amplitude reduction > velocity slowing)
• Needle EMG: denervation in distal muscles, chronic changes

Diabetic Amyotrophy Findings

• Active denervation in proximal leg muscles (vastus lateralis, iliopsoas, adductors)
• May see paraspinal involvement
• Sensory studies may be relatively preserved early
• Can look like radiculopathy or plexopathy

Small Fiber Neuropathy

• Standard nerve conduction studies may be NORMAL
• Skin biopsy showing reduced intraepidermal nerve fiber density is gold standard
• Quantitative sensory testing may be helpful

Mononeuropathies

• Focal abnormalities at common entrapment sites
• Diabetics more susceptible to entrapment neuropathies
• May have superimposed DSPN

Important Points

• Always compare to age-matched normal values
• Consider concurrent conditions (B12 deficiency, alcohol, medications)
• Serial studies can monitor progression

Recommendations

Glycemic Control

• Tight glucose control prevents and slows progression
• Target HbA1c less than 7% (individualized)
• More important for prevention than reversal

Pain Management

• First line: Pregabalin, Duloxetine, Gabapentin
• Second line: Tricyclic antidepressants (amitriptyline, nortriptyline)
• Topical: Capsaicin cream, Lidocaine patches
• Opioids: reserved for refractory cases
• Combination therapy often needed

Foot Care

• Daily foot inspection
• Proper footwear
• Regular podiatry visits
• Treatment of foot deformities
• Patient education critical

Risk Factor Modification

• Blood pressure control
• Lipid management
• Smoking cessation
• Weight management
• Alcohol moderation

Physical Therapy

• Balance training
• Strengthening exercises
• Gait training
• Fall prevention

Monitoring

• Annual foot exams
• Monofilament testing
• Regular HbA1c monitoring
• Screen for other complications (retinopathy, nephropathy)

What else could it be?

• B12 Deficiency: can coexist, check B12 and methylmalonic acid
• Alcoholic Neuropathy: similar pattern, different history
• Chronic Inflammatory Demyelinating Polyneuropathy (CIDP): demyelinating pattern, progressive, treatable
• Chemotherapy-Induced Neuropathy: history of chemotherapy
• Hereditary Neuropathies (CMT): family history, foot deformities from young age
• Uremic Neuropathy: check kidney function
• Hypothyroidism: check TSH
• Vasculitic Neuropathy: mononeuropathy multiplex pattern, systemic symptoms
• Paraproteinemic Neuropathy: check SPEP, UPEP
• Amyloid Neuropathy: autonomic features, cardiac involvement