What are the causes of reduced vibratory sensation?

Causes of Reduced Vibratory Sensation

The most common causes of reduced vibratory sensation are diabetic peripheral neuropathy, vitamin B12 deficiency, and chemotherapy-induced peripheral neuropathy, with diabetes being the predominant etiology in clinical practice.

Pathophysiological Mechanisms

Reduced vibratory sensation occurs due to damage to large-diameter sensory nerve fibers that transmit proprioceptive and vibratory information. This typically manifests as a length-dependent process, affecting the distal extremities first and progressing proximally.

Major Causes

1. Metabolic Disorders

• Diabetes Mellitus
  • Most common cause in clinical practice
  • Presents as length-dependent sensory polyneuropathy
  • Affects both small and large fibers, with large fiber dysfunction manifesting as reduced vibratory sensation 1
  • Typically begins in the distal lower extremities and progresses proximally
  • Often accompanied by loss of ankle reflexes and proprioception

2. Nutritional Deficiencies

• Vitamin B12 Deficiency
  • Causes demyelination in both central and peripheral nervous systems
  • Results in subacute combined degeneration of the spinal cord
  • Presents with reduced vibratory sensation, proprioception loss, and paresthesias 1
  • Often affects elderly patients (60-70 years) due to decreased absorption 2
  • Associated with cognitive changes, gait ataxia, and weakness
  • May present with neurological symptoms even with normal hematological parameters

3. Medication/Toxin-Induced

• Chemotherapy-Induced Neuropathy

  • Particularly with bortezomib and thalidomide
  • Bortezomib causes predominantly sensory neuropathy with reduced vibratory sensation 1
  • Thalidomide affects deep vibratory sensitivity and proprioception after prolonged exposure 1
  • Often dose-dependent and can persist after discontinuation

• Other Neurotoxic Medications

  • Antiretrovirals
  • Isoniazid
  • Metronidazole
  • Heavy metals (lead, arsenic, mercury)
  • Excessive alcohol consumption

4. Infectious/Inflammatory

• Lyme Disease

  • Can cause peripheral neuropathy with reduced vibratory sensation 1
  • Often presents with radicular pain and paresthesias
  • Typically shows reduced vibratory sensation in distal lower extremities

• Chronic Inflammatory Demyelinating Polyneuropathy (CIDP)

  • Progressive or relapsing immune-mediated neuropathy
  • Affects both motor and sensory functions
  • Often presents with symmetric weakness and sensory loss

5. Hereditary Neuropathies

• Charcot-Marie-Tooth Disease
  • Progressive hereditary motor and sensory neuropathy
  • Early manifestation includes reduced vibratory sensation
  • Often accompanied by foot deformities and distal weakness

Clinical Assessment

Assessment of vibratory sensation should be performed using a 128-Hz tuning fork, starting at the distal aspect of the hallux bilaterally and moving proximally until sensation is detected 1. This should be part of a comprehensive neurological examination that includes:

1. Small-fiber function: pinprick and temperature sensation
2. Large-fiber function: vibration perception and reflexes
3. Protective sensation: 10-g monofilament testing 1

Diagnostic Approach

When reduced vibratory sensation is detected:

1. Screen for diabetes - HbA1c, fasting glucose
2. Check vitamin levels - B12, folate, vitamin E
3. Review medication history - Identify potential neurotoxic agents
4. Consider specialized testing:
   • Nerve conduction studies for pattern and severity
   • Methylmalonic acid and homocysteine levels if B12 deficiency is suspected despite normal B12 levels

Clinical Pearls

• Reduced vibratory sensation often precedes other sensory deficits in many neuropathies
• Vitamin B12 deficiency can cause neurological symptoms even with normal hemoglobin levels 2
• Elderly individuals are more sensitive to marginal folate deficiency and relatively less responsive to repletion than younger adults 1
• In diabetic patients, annual assessment of vibratory sensation is recommended to identify those at risk for foot ulceration 1

Treatment Considerations

Treatment should target the underlying cause:

• Optimize glycemic control in diabetic neuropathy 1
• Vitamin B12 supplementation for deficiency states 3
• Dose reduction or discontinuation of offending medications when possible
• Pain management for symptomatic relief when appropriate

Remember that early identification of reduced vibratory sensation is crucial for preventing complications, particularly in diabetic patients where it can help identify those at risk for foot ulceration and amputation.