Peripheral Neuropathy Flashcards
Components of Peripheral Nerves
Adrenergic Fibers
Efferent Fibers
Afferent Fibers
Adrenergic fibers - nerve fibers, usually sympathetic, that liberate epinephrine or related substances as neurotransmitters.
Afferent fibers , Afferent nerve fibers - nerve fibers that convey sensory impulses from the periphery to the central nervous system.
Efferent fibers , Efferent nerve fibers - nerve fibers that convey motor impulses away from the central nervous system toward the periphery.
Axons
Parasympathetic Fibers
Postganglionic Parasympathetic Fibers
Axon -that process of a neuron by which impulses travel away from the cell body; at the terminal arborization of the axon, the impulses are transmitted to other nerve cells or to effector organs. Larger axons are covered by a myelin sheath.
Parasympathetic fibers - slow the heart; stimulate peristalsis; promote the secretion of lacrimal, salivary, and digestive glands; induce bile and insulin release; dilate peripheral and visceral blood vessels; constrict the pupils, esophagus, and bronchioles; and relax sphincters during micturition and defecation.
Postganglionic parasympathetic - fibers extend to the uterus, vagina, oviducts, and ovaries in females and to the prostate, seminal vesicles, and external genitalia in males, innervating blood vessels of pelvic organs in both sexes; stimulation of these nerves causes vasodilation in the clitoris and labia minora and erection of the penis
3 Types of Peripheral Neuropathy
- Mononeuropathy: Infarction and/or compression of nerve (carpal tunnel, sciatica)
- Polyneuropathy: Axonal degeneration (DM)
- Polyneuropathy: Segmental demyelination (MS)
Hx
Rate of onset and progression
Exposure to known toxin (e.g., metals, solvents, glue)
Drugs (e.g., quinine derivatives, phenytoin, glutethimide, gold, hydralazine, isoniazid, nitrofurantoin, vincristine)
Immunizations (e.g., influenza, rabies, typhoid, smallpox, etc.)
Recent infection
Malignancy
Family History
Symmetry
Symptoms distal, proximal, or mixed
Mononeuropathy Clinical Presentation
- Loss of motor and/or sensory function in distribution of one nerve or asymmetrically in multiple nerves (mononeuropathy multiplex)
- Loss of appropriate reflex(es)
- Pain may or may not be present.
- Not symmetrical and confined to 1 area
Polyneuropathy Clinical Presentation
- Loss of motor and/or sensory function, symmetrically (stocking/glove distribution), usually in the longest nerves first.
- Loss of reflexes, longest nerves first
- Pain may or may not be present.
- Symmetrical/Bilateral
Dying Back Rule
Length Rule
Dying Back - In Polyneuropathy - The most distal portions of axons are usually the first to degenerate, and axonal atrophy advances slowly towards the nerve’s cell body
Length Rule - As shorter nerves are affected, symptoms unroll up the leg as long as a stocking and from the hand up the arm as a long glove
PE
To differentiate peripheral from central nervous system lesions.
Neuro exam as indicated from history
Sensory: pain sensation (pin prick), light touch sensation (brush), position sense, stereognosia, graphesthesia, and extinction
Vibratory sense on distal boney prominence using 512-Hz tuning fork
Reflexes: + Babinski = CNS disease, is key to compare the strength of reflexes elicited with each other. A finding of 3+, brisk reflexes throughout all extremities is a much less significant finding than that of a person with all 2+, normal reflexes, and a 1+, diminished left ankle reflex suggesting a distinct lesion
Labs
Blood sugar
CBC with exam of peripheral smear and RBC indices
Serum folate and B12
LFT’s
BUN/Creatinine
Chest X-ray
Thyroxine and thyroid stimulating hormone
Toxic screen of blood, urine or hair as indicated for arsenic, lead, mercury or thallium
Dx Tests
Electrophysiologic studies
Nerve conduction velocity
Sensory latencies
Late responses (H&F)
Electromyography
CSF examination for protein, cells (including cytology)
Serum protein electrophoresis
Anti Hu antibodies: if suspected/known malignancy
Mononeuropathy Compression Diseases
sometimes related to amyloid, acromegaly and hypothyroidism
Carpal tunnel (median)
Peroneal
Radial
Ulnar
Lateral femoral cutaneous (meralgia paresthetica)
Many others
Mononeuropathy
Mononeuritis & Mononeuritis Multiplex Diseases
Vasculitis (e.g., SLE, polyarteritis)
Vasculopathy (e.g., diabetes mellitus)
Hyperviscosity (e.g., Waldenstrom, multiple myeloma, polycythemia)
Toxic (e.g., lead)
Infectious (e.g., Herpes zoster, leprosy)
Idiopathic (e.g., Bell palsy)
Paralysis of C.N. VII (facial nerve)
Polyneuropathy
Segmental Demyelination Diseases
Post infectious or post immunization (Landry-Guillain-Barre-Strohl syndrome, also known as acute inflammatory demyelinating polyneuropathy [AIDP])
Chronic inflammatory demyelinating polyneuropathy (CIDP)
Metachromatic leukodystrophy, Krabbe’s, etc.
Genetically determined (e.g., Charcot-Marie-Tooth)
Polyneuropathy
Axonal Degeneration Diseases
Vitamin deficiencies often associated with alcoholism (e.g., thiamine,B6, ?B12, folate)
Diabetes mellitus
Hepatic failure
Renal failure
Paraneoplastic (e.g., small cell lung cancer, myeloma)
Diphtheria
Amyloidosis (primary or secondary)
Porphyria Toxins (e.g., heavy metals, drugs)
Genetically determined (e.g., Friedreich’s ataxia)
Immune mediated (i.e. associated with monoclonal gammopathy of unknown significance (MGUS)
Idiopathic (e.g., motor system diseases) m. osteosclerotic myeloma may produce POEMS (polyneuropathy,organomegaly, endocrinopathy, monoclonal gammopathy and skin changes) syndrome
Tx
Treat underlying condition (e.g., vitamin deficiency, diabetes, intoxications, malignancy)
Steroids - Bell palsy, CIDP
Plasmapheresis for Guillain-Barre, CIDP and perhaps paraneoplastic neuropathies
IV immunoglobulin possibly effective for Guillain-Barre, CIDP and paraneoplastic neuropathies
Hospitalization and respiratory support for acute post-infectious polyneuropathy with plasma exchange in rapidly worsening cases
Genetic counseling
