Diagnostic Pathways for Idiopathic Neuropathy

Updated October 10, 2026: Clarified that skin biopsies look for small fibre neuropathy and are used when symptoms point that way, corrected the description of AIDP (the most common type of Guillain-Barré syndrome, not a synonym for all of it), and added that symptoms of an idiopathic neuropathy can still be treated even when no cause-specific treatment exists.

“You have a serious illness of an undisclosed nature” says a doctor to a patient in a cartoon within Dr. Norman Latov’s recent presentation on idiopathic neuropathy sponsored by the Foundation for Peripheral Neuropathy. There are many cases where people present neuropathic symptoms, but the causes are unclear.

Repeated nerve conduction testing may surface more clues as well as nerve and muscle biopsy.

The current diagnostic pathways Dr. Latov maps out are familiar and simple:

1. Electrodiagnostic (EDX) studies for people presenting the usual clinical symptoms of a neuropathic disease or disorder.
   • If results are normal, skin biopsies may reveal damage to the smallest nerve fibres (small fibre neuropathy), which a skin biopsy from the lower leg can reliably diagnose when symptoms and the examination point that way.¹
   • If results are abnormal, they will indicate predominantly axonal damage or demyelination.
2. Test for known causes of either demyelination or axonal damage.

Known Causes

If a known cause is identified, it may be treatable or untreatable.

• Immune mediated:
  • Acute Inflammatory Demyelinating Polyradiculoneuropathy (AIDP), the most common type of Guillain-Barré Syndrome (GBS)²
  • Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) (Neurological disorder)
  • Multifocal Motor Neuropathy (MMN) (Immune-mediated motor nerve disorder)
  • MAG Neuropathy (Autoimmune disorder)
  • POEMS Syndrome (Blood disorder)
• Autoimmune:
  • Axonal Guillain-Barré
  • Sjögren
  • Vasculitis
  • Celiac Disease
  • Sarcoid
• Hereditary Demyelinating or Axonal Neuropathies:
  • Some CMT, distal hereditary motor neuropathy (dHMN)
• Drug-Induced:
  • Amiodarone
  • Chemotherapy
  • INH
  • Checkpoint Inhibitors
• Endocrine and Metabolic:
  • Diabetes
  • Hypothyroid
  • Kidney failure
• Infectious:
  • Lyme
  • Hepatitis C
  • HIV-1/2
• Paraneoplastic:
  • Associated with Cancer (Lung, Lymphoma, Myeloma, IgM Monoclonal Gammopathies)
• Nutritional:
  • Alcohol Toxicity
  • B12 or B1 Deficiency
  • B6 Deficiency or Toxicity
• Toxic:
  • Lead
  • Mercury (Seafood)

If the Cause Is Idiopathic

• If a known cause is not identified, the “idiopathic” diagnosis remains with no treatment aimed at a specific cause. Symptoms can still be treated, though: nerve pain with medications such as certain antidepressants, gabapentin, or pregabalin, or with lidocaine patches or capsaicin cream, and walking problems with braces and orthopedic shoes.³
• If CIDP is diagnosed, it is treatable.

Stable vs. Progressive Neuropathy

• If the neuropathy is stable, it could be residual symptoms from a past insult, GBS, CIDP in remission, Lyme disease, acute viral illness, drug or toxin induced, other inflammatory conditions. This is common in small fibre neuropathies.
• If the neuropathy is progressive, diagnosis can be missed if not tested for. It could be an as yet unidentified genetic mutation, non-systemic vasculitis or sarcoidosis, atypical CIDP not meeting EDX criteria, or primary (light chain) amyloidosis. (Progression is best determined by EDX studies. Sensory symptoms are less consistent and reliable than motor functions. Fluctuating symptoms most often indicate a stable underlying neuropathy and are due to environmental or other factors. Test grip strength, walking speed, and leg strength.)
• Repeated nerve conduction testing may surface more clues as well as nerve and muscle biopsy.

Dr. Latov is not a proponent of any alcohol use. He notes that alcohol (especially in significant amounts) is a neurotoxin and doesn’t help anyone’s nervous system apart from the brief, enjoyable effects of intoxication.

Notes

1. Lauria, G., S. T. Hsieh, O. Johansson, et al. 2010. “European Federation of Neurological Societies/Peripheral Nerve Society Guideline on the Use of Skin Biopsy in the Diagnosis of Small Fiber Neuropathy.” European Journal of Neurology 17 (7): 903–12. https://doi.org/10.1111/j.1468-1331.2010.03023.x. ↩︎
2. National Institute of Neurological Disorders and Stroke. n.d. “Guillain-Barré Syndrome.” Accessed October 10, 2026. https://www.ninds.nih.gov/health-information/disorders/guillain-barre-syndrome. ↩︎
3. National Institute of Neurological Disorders and Stroke. n.d. “Peripheral Neuropathy.” Accessed October 10, 2026. https://www.ninds.nih.gov/health-information/disorders/peripheral-neuropathy. ↩︎