What are the causes of sensory motor neuropathy?

Causes of Sensory Motor Neuropathy

Sensory motor neuropathy has multiple etiologies including diabetes, vitamin deficiencies, toxins, medications, autoimmune conditions, infections, and paraproteinemias, with diabetes being the most common identifiable cause. Understanding these causes is crucial for proper diagnosis and treatment.

Common Causes

Metabolic and Endocrine Disorders

• Diabetes mellitus: Most common cause of sensory motor neuropathy, affecting up to 50% of diabetic patients 1, 2
• Hypothyroidism
• Uremia/chronic kidney disease

Nutritional Deficiencies

• Vitamin B12 deficiency: Can cause primary sensory demyelinating neuropathy 3
• Vitamin B1 (thiamine) deficiency
• Vitamin B6 (both deficiency and toxicity from excessive intake) 4
• Vitamin E deficiency
• Copper deficiency
• Folate deficiency

Toxic Exposures

• Alcohol: Common cause of axonal sensorimotor neuropathy
• Medications:
  • Chemotherapeutic agents (taxanes, platinum compounds, vinca alkaloids, thalidomide, bortezomib) 2, 5
  • Antibiotics (metronidazole, isoniazid, nitrofurantoin)
  • Antiretrovirals
  • Amiodarone
  • Phenytoin
• Industrial toxins (heavy metals, organic solvents)

Infectious Causes

• HIV: Can cause distal symmetric polyneuropathy
• Hepatitis C virus: Up to 50% of patients may develop neuropathy 2
• Leprosy
• Lyme disease
• Diphtheria

Immune-Mediated Disorders

• Guillain-Barré syndrome: Acute inflammatory demyelinating polyradiculoneuropathy 1
• Chronic inflammatory demyelinating polyneuropathy (CIDP)
• Vasculitic neuropathy
• Paraneoplastic neuropathies
• Anti-MAG antibody neuropathy 1, 2

Paraproteinemias and Hematologic Disorders

• Monoclonal gammopathy of undetermined significance (MGUS)
• Waldenström's macroglobulinemia: Can present with sensorimotor neuropathy 1
• Multiple myeloma
• Amyloidosis
• Cryoglobulinemia

Hereditary Causes

• Charcot-Marie-Tooth disease
• Hereditary sensory and autonomic neuropathies
• Familial amyloid polyneuropathy

Inflammatory Bowel Disease-Associated

• Peripheral neuropathy can rarely be associated with inflammatory bowel disease 1

Clinical Presentation Patterns

Sensory motor neuropathy typically presents with:

• Stinging sensations, numbness, and paresthesia in a stocking-and-glove distribution 2
• Positive sensory symptoms with impaired proprioception and vibratory sensitivity
• Pain that doesn't subside between episodes
• Motor impairment in approximately 10% of cases 2
• Orthostatic hypotension as the most common autonomic manifestation 2

Diagnostic Approach

1. Laboratory testing:

   • Complete blood count
   • Comprehensive metabolic panel
   • HbA1c
   • Vitamin B12, folate, and other vitamin levels
   • Thyroid function tests
   • Serum protein electrophoresis and immunofixation
   • Hepatitis B, C, and HIV testing 2
   • Anti-MAG antibodies if demyelinating features present 2

2. Electrophysiological studies:

   • EMG and nerve conduction studies to confirm axonal pattern and quantify severity 2
   • Characteristic findings include low amplitude sensory action potentials with relative preservation of nerve conduction velocities 2

3. Additional testing as indicated:

   • Skin biopsy with intraepidermal nerve fiber density assessment (especially for small fiber neuropathy) 2
   • Cerebrospinal fluid analysis
   • Nerve biopsy (rarely indicated)

Treatment Considerations

Treatment depends on the underlying cause:

• Diabetes: Strict glycemic control 2
• Vitamin deficiencies: Appropriate supplementation
• Toxic/medication-induced: Removal of offending agent
• HCV-related: Antiviral therapy 2
• HIV-related: Optimization of antiretroviral therapy 2
• Paraproteinemic: Rituximab, IVIG, or plasma exchange 2
• Neuropathic pain: Pregabalin, gabapentin, or duloxetine 1, 2

Important Caveats

• Peripheral neuropathy is a diagnosis of exclusion; nondiabetic neuropathies may be present in patients with diabetes and may be treatable 1
• Up to 50% of diabetic peripheral neuropathy may be asymptomatic 1
• Rapid correction of glucose levels in diabetic ketoacidosis can sometimes trigger acute neuropathy 6
• Some toxic neuropathies can present acutely, mimicking Guillain-Barré syndrome 7
• Consider rare causes such as excessive vitamin intake (e.g., vitamin B6 toxicity) 4

By systematically evaluating patients with sensory motor neuropathy and identifying the underlying cause, appropriate treatment can be initiated to prevent progression and potentially reverse neurological damage.