#29 Neuropathy Deconstructed

March 6, 2017 | By Matthew Watto, MD

Stop the madness! Diagnose and treat neuropathy like expert guest, Dr. Grace Kimbaris, Assistant Professor of Clinical Neurology from University of Pennsylvania. We cover the basics along with some random pearls on fluoroquinolones, small fiber neuropathy, alpha lipoic acid, and more! 

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Clinical Pearls:

1. Neuropathy is a nonspecific term with multitude of causes
2. Take a good history e.g. previous chemotherapy, alcohol use, gastric bypass, family history of neuropathy, CKD, chronic liver disease
3. Red flags symptoms: Predominant motor symptoms, Asymmetry, Rapid onset or progression (e.g. weeks to months instead of years), Family history of neuropathy, Autonomic symptoms e.g. syncope, sweating, urinary or sexual dysfunction, impaired digestive function, exercise intolerance (lack of heart rate variability)
4. Radiculopathy – nerve affected at level of nerve root exiting spinal canal by any cause  e.g. inflammation, or mechanical compression
5. Mononeuropathy –  single nerve affected e.g. carpal tunnel syndrome = median nerve mononeuropathy
6. Distal symmetric polyneuropathy (DSP): Length dependent. Starts in lower extremities and progresses slowly upward over months to years (stocking and glove).
7. DSP diagnosis: glucose tolerance test (or A1C), B12 level, SPEP with immunofixation electrophoresis.
8. EMG: measures larger, faster conducting fibers
9. Large fiber neuropathy: Affects vibration sensation, proprioception, and/or motor function. EMG is abnormal.
10. Small fiber neuropathy: Involves nerves for pain (pin prick) and temperature sensation. EMG is normal. Usually length dependent and symmetric with significant pain symptoms. Diagnosed by skin punch biopsy at bedside.
11. Fibromyalgia: a certain percentage of these patients may be misdiagnosed and actually have small fiber neuropathy.
12. Topical therapy: Lidocaine for diabetic neuropathy. Capsaicin for post-herpetic neuralgia.
13. Oral therapy: tricyclic antidepressants, gabapentinoids (gabapentin, pregabalin),  duloxetine, venlafaxine. Start low and go slow.
14. Alpha lipoic acid 600 mg once daily reasonable to trial for diabetic neuropathy.

Goal: Listeners will learn to identify, classify, and treat distal symmetric polyneuropathy (DSP).

Learning objectives:
By the end of this podcast listeners will:

1. Define the common terms used to describe neuropathy
2. Recognize importance of past medical history in diagnosis
3. Differentiate and classify type of neuropathy based on exam and lab findings
4. Implement a basic approach to managing DSP
5. Identify patients with small fiber neuropathy

Disclosures:
Dr. Kimbaris reports no relevant financial disclosures.

Time Stamps

00:00 Intro
01:30 Picks of the week
09:42 Wikipedia style definition of neuropathy
12:50 Workup of distal symmetric polyneuropathy
15:20 Relationship of impaired glucose regulation and neuropathy
17:28 Fluoroquinolones and neuropathy
21:16 Red flag symptoms
25:36 Large versus small fiber neuropathy
31:47 Controversy over small fiber neuropathy
36:35 B12 deficiency
39:07 Treatment of painful neuropathy
43:00 Alpha lipoic acid
46:10 Take home points
48:12 Outro

Picks of the week:

1. The Night Manager Season 1 on Amazon Prime
2. The Witch (film) by Robert Eggers on iTunes
3. The One Thing: The Surprisingly Simple Truth Behind Extraordinary Results (book) by Gary Keller with Jay Papasan
4. Lincoln on Leadership: Executive Strategies for Tough Times (book) by Donald T. Phillips

Links from the show:

1. Callaghan BC, Price RS, Feldman EL. Distal Symmetric Polyneuropathy: A Review. JAMA. 2015 Nov 24;314(20):2172-81. doi: 10.1001/jama.2015.13611.
2. FDA Warning on Fluoroquinolones from July 2016
3. Neurology. 2014 Sep 30;83(14):1261-3. doi: 10.1212/WNL.0000000000000846. Epub 2014 Aug 22. Oral fluoroquinolone use and risk of peripheral neuropathy: a pharmacoepidemiologic study. Etminan M1, Brophy JM2, Samii A2.
4. Pain. 2013 Nov;154(11):2310-6. doi: 10.1016/j.pain.2013.06.001. Epub 2013 Jun 5. Objective evidence that small-fiber polyneuropathy underlies some illnesses currently labeled as fibromyalgia. Oaklander AL1, Herzog ZD, Downs HM, Klein MM.

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