But why
Name 4 causes of polyneuropathy
Toxins - heavy metals
Drugs - chemotherapy, alcohol
Deficiency - Vitamin B6 deficiency
Metabolic - uremic, diabetes
Hereditary
Infectious
Autoimmune - AIDP, CIDP
Polyneuropathies as a whole can be divided into these 2 main types.
Inherited and acquired
Regarding chronic demyelination: prolonged distal latency of 2 more nerves at non entrapment sites of > ____ % of the ULN and conduction velocity < ____ % of LLN fulfill 2/4 criteria
130% and 75%
This is the best predictor of a poor outcome or prolonged course of GBS patients.
Low CMAP amplitudes (< 20% of the LLN from weeks 3-5)
Is this conduction block or axonal degeneration, as axonal degeneration is now considered hallmark to poor prognosis.
A 25 year old avid runner presents with plantar pain worse on weight bearing and slightly worse on her right foot. NCS shows normal right peroneal and tibial amplitude with prolonged latency; normal amplitude sural with prolonged latency; prolonged F waves; normal median sensory amplitude and latency. What would you do next?
Warm her feet and retest. She has plantar fasciitis.
Diabetes is the most common cause of polyneuropathy. Name one pathophysiological reason for this.
Microcirculatory disorders
Impaired mitochondria and lipid metabolism
Activation of alternative metabolic pathways
Neurotoxic glycated protein formation
These are the 5 general questions you want aim to answer in your classification of the polyneuropathy.
1. time course: acute, subacute, chronic, progressive, stepwise, relapsing-remitting
2. Fiber type: motor, large sensory, small sensory, autonomic
3. Pattern: distal predominant, multiple nerves, asymmetric, symmetric
4. Nerve pathology: axonal, demyelinating, mixed, if able what is primary
5. Severity: slightly subjective, many different scales, if see EMG changes with lifestyle changes due to risk of falls walking difficulty, balance concerns
A young male patient presents acutely with weakness. A present but prolonged F wave of >___% of ULN would be supportive of an acute demyelinating pathologic finding.
125%
A 60 year old with history of alcohol abuse in his problem list presents with burning feet for "Years doc" and commenting frequently that he falls all the time as if his "feet feel like they are attached". He is now abstinent, as of 3 months ago. A study classically would show evidence of an axonal or demyelinating, sensory or motor or sensorimotor neuropathy. Bonus: on the way out the door he asks you roughly how many alcoholics have these problems.
axonal sensorimotor
roughly 2/3 of chronic alcoholics
You find an absent peroneal nerve response with absent sural response and prolonged tibial llatency. What do you do next?
Test upper extremity nerve - radial nerve (nonentrapment nerve)
+
proximal stimulation in LE to show distal gradient
Typical NCS have limited utility when assessing these types of nerves
A delta and C fibers
This feature separates inherited from acquired demyelinating polyneuropathies.
absence of conduction block at non entrapment sites
This diagnostic finding differentiates multifocal motor neuropathy from ALS
motor conduction block - demyelination is not present in ALS. Need in 2+ nerves at nonentrapment sites.
MMN: age younger than 45, progressive weakness in distribution of peripheral nerve typically in upper extremity, men:woman ration 2:1
A 50 year old male presents with 4 months of numbness and weakness in hands and feet. Physical examination shows distal leg weakness and intrinsic hand muscles. Bicep and patellar reflexes are absent. NCS shows the slowed conduction velocities and prolonged distal latencies in the LE with absent peroneal and tibial F waves, partial peroneal motor block, and absent median sensory. The most likely diagnosis is ____.
CIDP
Progression over at least two months
Weakness more than sensory symptoms
Symmetric involvement of arms and legs
Proximal muscles involved along with distal muscles
Reduced deep tendon reflexes throughout
Increased CSF protein without pleocytosis
Nerve conduction evidence of a demyelinating neuropathy
Nerve biopsy evidence of segmental demyelination with or without inflammation
You find a borderline low 6 mV sural SNAP amplitude bilaterally in 35 yo woman with poorly managed type 1 diabetes and hypothyroidism with chronic sensory complaints. You are concerned you may be be missing something. What could you do to give yourself supporting information for a diagnosis?
calculate the sural radial amplitude ratio
< 0.21
A patient with severe limb and chest wall sensory abnormalities is most likely to have this type of polyneuropathy.
Axonal
Escutcheon sign - shield or emblem
This is factor (not official diagnosis) is the most common risk factor for developing polyneuropathy.
Impaired glucose tolerance
Patient X has a left peroneal amplitude at the ankle of 2 mV and 0.5 mV at the knee with distal latency 9.0 and velocity 25 m/s. What does this demonstrate?
partial motor conduction block, defined as >/= 50 % amplitude reduction of the proximal CMAP amplitude relative to distal, if distal CMAP amplitude is >/= 20 % of the LLN
A 68 year old male recently diagnosed with multiple myeloma recently completed his 4th round of chemotherapy 2 months ago of bortezomib, lenalidomide, dexamethasone. He reports ascending burning, shooting pain in his feet up to his knees and his hands most recently. This is the typical NCS: SNAP and CMAP and EMG findings if related to the bortezomib alone.
SNAP abnormal as typically presents as sensory alone in ~80% of cases.
Peaks after 5 rounds, but usually dose limiting.
Your are a PCP with a 60 yo type 2 diabetic patient describing classic diabetic polyneuropathy with no falls or near falls in at least the past 6 months. Do you refer for an EMG?
No
According to the AANEM, electrodiagnostic testing is likely to be low yield when:
symptoms and exam findings are mild, distal sensory predominant, has a known cause, and little concern for other nerves.
The most common inherited polyneuropathy typically starts in the first 2 years of life with stocking/glove pattern and results in intrinsic foot muscle wasting with pes cavus and hammer toes. This nerve pathology is found (broadly) and is a result of a duplication mutation in this gene.
Demyelinating and PMP22 duplication
These 3 tests are of highest yield in evaluating unknown etiology of a distal symmetric polyneuropathy.
Glucose evaluation, B12 (and metabolites), and SPEP
What needs to be studied to fulfill the billing code 95886 (complete needle EMG)?
Five or more muscles studied; innervated by 3+ nerves OR 4+ spinal levels
A 35 year old female with intermittent daylong fevers for the past 5 months presents with history of previous Right elbow pain then Left foot pain and now Right leg weakness. While not common, you find evidence of asymmetric axonal findings in upper and lower extremity nerves. What is the most likely diagnosis?
mononeuritis multiplex
You have diagnosed your patient with a severe length dependent symmetric sensorimotor polyneuropathy. Now what?
Educate them on secondary prevention