Management of Nutritional and Toxic Neuropathies


Nutritional and Toxic Neuropathies

1. Conditions causing nutritional neuropathies
2. Specific nutritional factors:
  • B1
  • B12
  • B6
  • Copper
  • Vitamin E

3. Toxic neuropathies: heavy metals (mercury), alcohol, medications
4. General considerations regarding work-up and management

Case Study

RussellChinStomach22554 y/o woman with diabetes, asthma, high blood pressure, morbid obesity (body mass index=65; weight=377 lbs)
10/2002: gastric bypass.  Post-op had nausea and vomiting with rapid weight loss
5/2003: tingling, numbness in feet, gait imbalance.  B12 deficiency suspected (not tested); started intramuscular injections
9/2003: respiratory distress, nausea/vomiting, abdominal pain. Weight=225 lbs.
10/2003: incoordination of hands, numbness, asymmetric limb weakness
X-ray showed enlarged heart and fluid in lungs, leading to insertion of a breathing tube
What is the cause? What should we test for?

Risk Factors for Malnutrition

1. Eating disorders (e.g., anorexia, bulimia)
2. Limited access (homelessness, low socioeconomic status)
3. Pregnancy-associated vomiting
4. Alcohol abuse
5. Medications: e.g., isoniazid, an antibiotic used to treat tuberculosis→B6 deficiency
6. Malabsorption:
  • Intentional (gastric bypass surgery, removal of part of small intestine)
  • Medical conditions affecting GI tract: irritable bowel disease, celiac disease, chronic liver/pancreatic disease, stomach irritation and inflammation

Neuropathy After Stomach Reduction Surgery for Treating Obesity

Various forms: bypass, adjustable band, sleeve gastrectomy

Neurologic complications:

Incidence: 0.08-16% found in one study and 4% in another

In review of 50 case reports (96 patients), most common findings were neuropathy (in 62%) and brain disorder (in 31%).

(Koffman et al., Muscle Nerve, 2006)

Risk factors for neuropathy occurring after stomach-altering surgery:
  • Increased levels of pre-op blood Hemoglobin A1c and triglycerides
  • Prolonged nausea/vomiting
  • Post-surgical complications
  • Rapid weight loss
  • Poor follow up at nutritional clinic
  • Reduced blood albumin/transferrin levels               

(Thaisetthawatkul et al., Muscle Nerve, 2010)

In a controlled study, neuropathy developed in 16% of stomach reduction surgery patients vs. 3% of patients who had gall bladder removal surgery.

Neuropathy subtypes:

  1. Sensory-predominant: secondary to nutritional deficiencies?
  2. Mononeuropathy, radiculoplexus neuropathy: more likely in setting of diabetes mellitus?

Immune-mediated cause in some patients?

(Thaisetthawatkul et al., Neurology, 2004)


Specific Nutritional Factors Associated With Neuropathy

  • B1 (thiamine)
  • B6 (pyridoxine)
  • B12
  • Copper cause
  • Vitamin E


Vitamin B1 (thiamine)RussellChinPregnant

Required for the action of 4 enzymes essential for sugar metabolism

Rapidly depletable (very little stored in body)

Absorbed in small intestine

Sources: whole grains, yogurt, protein foods, nuts, beans, soy

Recommended daily allowance is 1-1.5 mg/day; higher requirements in athletes, pregnancy, cancer

Diagnosis: measure the activity of the enzyme erythrocyte transketolase (better reflects body’s stores) or thiamine pyrophosphate

Treatment of deficiency: 100 mg daily either intravenous or orally

Neurologic signs:

Wernicke encephalopathy: eye changes, balance disturbance, mental confusion

Beriberi (severe deficiency) with/without heart failure (“wet” vs. “dry”)


  • “Burning foot” syndrome (acute/subacute, predominantly small/large fiber
  • sensory)
  • Motor-dominant (acute Guillain-Barré Syndrome-like, “dry” beriberi)
  • Cranial nerve involvement (weakness of tongue, facial and eye muscles)
Vitamin B6 (pyridoxine)

B6 deficiency OR excess can cause neuropathy. 

Deficiency is rare; usually due to pregnancy/lactation, general malnutrition (e.g., alcoholism), medications (B6 antagonists, e.g., isoniazid, hydralazine, penicillamine, 4-deoxypyridoxine, oral contraceptive pills), chronic dialysis

Sources: fish, beef liver, organ meats, potatoes, starchy vegetables, fruit (other than citrus), fortified cereals

Diagnosis: blood B6 or pyridoxal phosphate levels

Deficiency can cause:

  • Painful burning sensations, numbness in feet
  • Skin changes
  • Seizures (infants)

Treatment for deficiency: <50 mg/day (U.S. RDA=2 mg). Avoid excess!


Neuropathy due to EXCESS B6RussellChinB6200_0

Source: homeopathic cold remedies, excess supplementation, energy drinks. 

Burning sensations and balance issues described in patients taking 2 grams/day

(Schaumburg et al., N Engl J Med, 1983)

Also reported in patients taking minimum of 200 mg/day

(Parry and Bredesen, Neurology, 1985)

All improved after discontinuing B6

Model of isolated sensory neuropathy without systemic disease


Vitamin B12RussellChinB12350

B12: important for myelin sheath (nerve fiber insulation) formation due to

formation of:

1. methionine, tetrahydrofolate;

2. succinyl coenzyme A.

Source: meat/dairy products, fortified foods, supplements

Complex metabolism

Absorbed in terminal ileum

Up to 40% of older adults have low blood B12 levels. 

Normal blood values=250-1100 pg/mL; target>400 pg/mL

Vitamin B12 Deficiency

Causes of deficiency:

  • Pernicious anemia (immune destruction of intrinsic factor, a protein made in the stomach that is required for B12 absorption.  This can cause low red blood cell count with some enlarged red blood cells, which is called megaloblastic anemia.)
  • Vegan diet (can take 5 yrs to manifest)
  • Medications (proton pump inhibitors, metformin),
  • Food-cobalamin malabsorption (due to nitrous oxide exposure [inactivates methyl-cobalamin])

Diagnosis: low B12, elevated methylmalonic acid (MMA) level

Renal disease→false positive MMA elevation

Homocysteine elevation: less specific (also seen with hypothyroidism, folate and vitamin B6 deficiency, advanced age, cigarette smoking)

Additional testing: intrinsic factor and parietal cell antibodies?

Neurologic syndromes associated with B12 deficiency

1. Neuropsychiatric abnormalities

2. Subacute combined degeneration of the spinal cord with involvement of:

  • Dorsal columns: loss of sense of position, shown by loss of balance when patient stands with feet together and eyes closed
  • Lateral columns: corticospinal weakness (e.g., hip, knee flexors) spastic partial paralysis
  • Reflexes: mixed with absent ankle reflexes and brisk knee and ankle reflexes

3. Neuropathy: typically sensory axonal neuropathy +/- damage to spinal cord 

  • Acute onset, upper +/- lower extremity involvement=clues to diagnosis 
  • Megaloblastic anemia may NOT be present in patients with neuro manifestations

4. Damage to the nerve to the retina of each eye

B12 deficiency treatmentRussellChinB12Def                       

  1. Oral: 1000 mcg/day (1%, or 10 mcg; RDA=3-6 mcg/day.)  
  2. Intramuscular injections: 1000 mcg daily X 3-7 days or 1000 mcg weekly X 4, then maintenance with 1000 mcg monthly.
  3. Intranasal (Nascobal): 500 mcg weekly 

Oral as effective as IM?    

(Vidal-Alaball et al., Cochrane Database Syst Rev, 2005)

Muscle injection is preferable in pernicious anemia, or with a history of gut malabsorption

Neurologic improvement expected in first 6 months;

May only prevent further neurologic deterioration. 

B3 (niacin, nicotinic acid)

Classic clinical triad: skin inflammation, dementia, diarrhea.

Absorbed in intestine via simple diffusion

Risk factors: homelessness, anorexia, certain cancers, malabsorption

Neurologic manifestations: apathy, inattention, irritability, depression. 

Not known to be a cause of neuropathy. 

Treatment: 50 mg 2-3 times/day.  


Component of important enzymes

(e.g., cytochrome C oxidase) for ATP production,

antioxidation, neurotransmitter production,

and cross-linkage of collagen and elastin. 

Sources: seafood, nuts, wheat, grains

Absorbed in stomach and proximal duodenum via active or passive mechanisms (depending on dietary levels). 

Gastric acid required to solubilize dietary copper. 

In liver, copper incorporated into ceruloplasmin for delivery to cells.  (Liver excretes excess copper into bile.)

Zinc→upregulation of metallothionein in enterocytes which binds copper→sloughed off in feces.

Copper deficiency→myelopathy or myeloneuropathy

(Kumar et al., Neurology, 2004)

Also hematologic abnormalities: anemia, occasionally myelodysplastic syndrome. 

Causes: gastric surgery, excess zinc (supplements or older denture creams), poor diet, clioquinol or idiopathic. 

Copper deficiency causing myeloneuropathy (damage to spinal cord as well as peripheral nerves)

Mimics subacute combined degeneration (sensory ataxia due to dorsal column dysfunction, corticospinal tract weakness, lower limb spasticity)

Gait difficulties

Abnormal sensations in skin of lower limb, such as pins and needles, numbness or burning

Dorsal column: loss of position sense, vibration, loss of balance

Lateral column: corticospinal-pattern weakness, spasticity, brisk knee reflexes, extensor plantar responses. 

MRI of the spine shows changes in parts of the spinal cord in the neck or thorax in ~50% of cases

(Jaiser & Winston, J Neurol, 2010)

Copper deficiency

Diagnosis: check blood and urine zinc, copper, blood ceruloplasmin. 

RDA=900 mcg/day.

Expected values in deficiency: 
  • Low blood copper
  • Low ceruloplasmin
  • 24-hr urine: low copper (more sensitive than blood level)
  • Zinc level in blood/urine: normal or high (if exogenous source)

Treatment: 2 mg elemental copper three times a day  


Vitamin E

Alpha-tocopherol=biologically active form of vitamin E in humans, fat-soluble.

Sources: animal fat, vegetable oils, nuts, grains

Incorporated into chylomicrons, passively absorbed in intestines.

Vitamin E delivered to tissues via chylomicrons.

Transferred to very VLDL lipoproteins via alpha-tocopherol transfer protein (TTP). 

Deficiency: malabsorption or transport deficiencies (mutations of transfer protein, abetalipoproteinemia), cystic fibrosis. 

Pathogenesis: due to loss of protective effect (antioxidant, free radical scavenger).

Neuro manifestations: ataxia, decreased reflexes, loss of sense of position or vibration, speech difficulty, involuntary eye movements, paralysis of eye muscles, damage to the retina, head shaking, decreased sensation and weaknessof muscles in the upper arms and legs. 

Nerve conduction studies show sensory-predominant, axonal neuropathy.   

Diagnosis: measure blood alpha-tocopherol levels, total blood vitamin E: total blood lipid concentration. 

Treatment: 400 IU twice daily, with dose increase until normalization.  Higher requirements in abetalipoproteinemia.  RDA=15 mg/day 


Case Study

RussellChinStomach22554 y/o woman with diabetes, asthma, high blood pressure, morbid obesity (body mass index=65; weight=377 lbs)
10/2002: gastric bypass.  Post-op had nausea and vomiting with rapid weight loss
5/2003: tingling, numbness in feet, gait imbalance.  B12 deficiency suspected (not tested); started intramuscular injections
9/2003: respiratory distress, nausea/vomiting, abdominal pain. Weight=225 lbs.
10/2003: incoordination of hands, numbness, asymmetric limb weakness
X-ray showed enlarged heart and fluid in lungs, leading to insertion of a breathing tube
What were the results?

Lab studies (October 2003, 2 wks after admission):

B1=0.8 (normal=1.6-4 microg/dL)

B6=2.7 (normal=5-30 ng/mL)

Folate=1 (low)

Anemia of chronic disease

Vitamin E: normal

B12 (=682): normal (receiving IM injections since May 2003). 

Spinal fluid protein is twice normal

Electromyogram/nerve conduction studies: axonal sensory and motor polyneuropathy 

Diagnosis: Neuropathy due to chronic malnutrition; Guillain-Barre syndrome-like presentation in setting of thiamine deficiency


Toxic neuropathies

Peripheral nervous system: high metabolic rate, vulnerable blood-nerve barrier

Dorsal root ganglia: especially vulnerable (no effective barrier)

Clinical features: neuropathies represented by sensory disturbances


1. Alcohol

2. Heavy metals: mercury, arsenic, lead

3. Medications: chemo, non-chemo (causal relationship clearly established in minority)

Alcohol-related neuropathy

Prevalence (chronic alcoholics): 4-30%RussellChinAlcohol

Including those with subclinical neuropathy: 9-67%

Pathogenesis: nutritional deficiency (e.g., thiamine) +/- direct toxic effect, multifactorial


  • Painful small fiber, sensory and autonomic dysfunction
  • Sensorimotor axonal (numbness, distal weakness, sensory ataxia)
  • Acute axonal (Guillain-Barré-like) with normal cerebrospinal fluid protein and more severe sensory symptoms


Mercury toxicity 

Effects on nervous system depend on chemical state 

Elevated blood methylmercury levels noted in idiopathic axonal neuropathy

Concentration and duration of exposure required for neurotoxicity, response to dietary intervention is unknown.

Larger prospective studies needed.                                                                   

(Latov et al., JAMA Neurology, 2015)







Peripheral neuropathy: rare but reported side effect.

Food and Drug Administration (2013) included risk of permanent neuropathy as side effect.

Increased risk reported

(Etiman et al., Neurology, 2014)


Muscle pain (at onset of use) is more typical

Association with peripheral neuropathy more controversial.

Some reports of small fiber sensory/autonomic neuropathy with mild clinical symptoms.


NO association between statins and neuropathy recently reported

(Svendsen et al., Br J Clin Pharmacol, 2017)



In the developed world:

Nutritional neuropathies in setting of inadequate diet, medications, alcohol, malabsorption (GI disease or bariatric surgery).

Toxic neuropathies due to alcohol, medications (chemo, non-chemo), alcohol, heavy metals (mercury?). 


Alcohol→thiamine deficiency, direct toxic effect

B6 EXCESS→sensory neuronopathy

B12 deficiency→subacute combined degeneration +/- peripheral neuropathy

Copper deficiency→neuropathy involving nerves of the spinal cord and periphery


These neuropathies are typically length-dependent (affecting lower legs and arms), sensory or sensorimotor, axonal. 

Repletion of deficiency or elimination of toxin may arrest progression, but recovery may be limited.