Peripheral Nervous System (PNS) Notes Fall 2024 PDF

The Peripheral Nervous System Goodman Ch 39 Fall 2024 Learning Objectives 1. Identify clinical signs and symptoms of PNS pathology. 2. Understand the relationship between myelin thickness and conduction velocity in sensory and motor nerves. 3. Describe the normal age-related changes that...

The Peripheral Nervous System Goodman Ch 39 Fall 2024 Learning Objectives 1. Identify clinical signs and symptoms of PNS pathology. 2. Understand the relationship between myelin thickness and conduction velocity in sensory and motor nerves. 3. Describe the normal age-related changes that occur in the PNS 4. Understand the difference between segmental and Wallerian degeneration in peripheral nerve injury. 5. Discuss the pathophysiology of selected hereditary neuropathies of the PNS. 6. Discuss the pathophysiology of selected compression and entrapment syndromes of the PNS. 7. Discuss the pathophysiology of selected infectious/inflammatory neuropathies. 8. Understand the clinical signs and symptoms of Complex Regional Pain Syndrome. Introduction Disorders of the PNS classified into 2 categories: Neuropathies Pathological condition confined to nerves Myopathies Pathological condition occurs in muscle Introduction Signs and symptoms of PNS disorders: Lower motor neuron involvement Anterior horn cell (cell body of α motor neuron) Axons arising from anterior horn (peripheral n.) Cranial nerves Motor end plate of axon Muscle fiber innervated by motor nerve  -wrap entire nerve -wrap each fascicle -wrap each axon Within a typical peripheral nerve only about 25% of fibers are myelinated Sites of peripheral nerve involvement MOTOR Motor neuron cell body Axon motor end plate Muscle fiber SENSORY Cell body in DRG Axon Sensory receptor Sunderland Classification of Nerve Injury Based Upon axonal and CT covering involvement Neurapraxia – segmental demyelination – Slows or blocks AP – Often occurs after nerve compression  temporary ischemia – When occurring because of disease (MS)  myelinopathy – Muscle typically does not atrophy because AP normal above and below site of injury – Schwann cells can become mitotically active to repair Sunderland Classification of Nerve Injury Based Upon axonal and CT covering involvement Axonotmesis – – Axon damaged…CT coverings remain intact – Prolonged compression  infarction and necrosis – Repair possible as long as nerve cell body intact – New axons “sprout” from damaged axon – Proximal and distal ends of CT “tube” must be intact Sunderland Classification of Nerve Injury Based Upon axonal and CT covering involvement Neurotmesis – most severe axonal loss – Complete severance of axon with disruption of CT coverings – Common with gunshot, stab wound, avulsion – Axonal continuity is lost  Wallerian degeneration – Muscle fibers innervated by axon rapidly atrophy and after 2 years undergo irreversible damage – Surgical intervention needed to reattach proximal and distal endoneurium (Without surgery  neuroma often forms) – Once axon has distal contact with muscle or sensory receptor…myelination can then begin – Repair process begins with “sprouting of new growth cone” as new cytoplasm is synthesized – Growth rate typically 1mm per day or 1 inch per month neurapraxia axonotmesis Problems with muscles Recap Neuropathy, myopathy Lower motor neuron involvement Sites of peripheral nerve involvement for motor and sensory nerve Conduction velocity depends on myelin and thickness of nerve Neurapraxia, axonotmesis, neurotmesis MU- Normal, segmental demyelination, axonal degeneration, myopathy Age Related ∆’s to PNS Perineurium and epineurium thicken Endoneurium fibrosis with ↑ collagen content Age does not affect size or # of fascicles Ventral root fibers (motor) more affected than dorsal root fibers (sensory) Myelin sheath deterioration (possibly by ↓ protein synthesis) Age Related ∆’s to PNS Atherosclerotic plaques may occlude vessels supplying nerves  loss of fibers  PERIPHERAL NEUROPATHIES ANS dysfunction – Excess lipofuscin in cells – Cells less efficient of ridding themselves of toxins – Sympathetic control of dermal vasculature declines Decreased wound healing Age Related ∆’s to PNS Axonal atrophy… – Decreased nerve Conduction Velocity (NCV) – Amplitude of action potential reduced (eg sensory nerve action potential (SNAP)) – Decreased intraaxonal transport – Shorter internode distance (segmental demyelinations and remyelinations) – S&S of peripheral neuropathy: Tingling in hands and feet Weakness in distal extremity muscles Gait instability from sensory losses Nerve Injury: Segmental demyelination – Axon remains intact, myelin breaks down – Caused by compression or disease Wallerian degeneration – Distal degeneration of an axon – Caused by crush, stretch, laceration, disease Neuropathy Mononeuropathy – One peripheral nerve affected Polyneuropathy – Several peripheral nerves affected Recap Age-related changes in PNS – Perineurium and epineurium thicken, – Endoneurium fibrosis, myelin deteriorates – Motor > sensory – Plaques occlude blood supply to nerve- Peripheral neuropathy – ANS dysfunction (decreased wound healing) – Axonal atrophy (decreased amp AP…) Nerve Injury-Segmental demyelination, Wallerian degeneration Neuropathy-Mono-, Poly-neuropathy Hereditary Neuropathies Charcot-Marie-Tooth Disease (CMT) Hereditary motor and sensory neuropathy (HMSN) Most common inherited disorder of sensory & motor nerves First described in 1880s by: – Jean Martin Charcot – Pierre Marie – Howard Henry Tooth Initial involvement of peroneal n. followed by muscles of foot & leg Hereditary Neuropathies Charcot-Marie-Tooth Disease (CMT) 1 in 2500 persons in US has some form of CMT CMT affects an estimated 2.6 million people (www.charcot- marie-tooth.org) Mostly autosomal dominant (CMT 1 and 2 – similar clinical presentations) CMT-1 - Causes mutations in proteins responsible for Schwann cell myelination in peripheral nerves Extensive demyelination with Schwann cell “bulb” formation (palpable) CMT 2 affects anterior horn cells and DRG of lumbar levels Hereditary Neuropathies Charcot-Marie-Tooth Disease (CMT) Slowly progressive Distal lower extremity symmetric weakness, atrophy, diminished DTR’s Weakness of dorsiflexors and evertors (steppage gait) Proprioception and cutaneous sensation lost in lower extremities (especially in CMT 1) Distal upper extremity sxs seen in later stages Hereditary Neuropathies Charcot-Marie-Tooth Disease (CMT) Video steppage gait patient perspective https://www.youtube.com/watch?v=Ma3Il942NEI https://www.youtube.com/watch?v=RR6GOatrPnA Hereditary Neuropathies Charcot-Marie-Tooth Disease (CMT) Treatment Symptomatic – maintain function in safe manner Orthotics for foot deformities Skin care essential (skin without sensation at risk of lesions) ROM exercises and stretches to prevent contractures Strengthening ex’s- Benefit secondary to slowly progressive and degenerative nature of disease Compression and Entrapment syndromes Carpal Tunnel Syndrome Most common entrapment neuropathy Characterized by… Pain Tingling Numbness Parasthesias Muscle weakness …in distribution of median n. Carpal Tunnel Syndrome Deep branch of ulnar n. FPL & ulnar artery FCR FDS Hypothenar Median N. muslces FDP Median nerve Wasting of: FPB OP APB Carpal Tunnel Syndrome Incidence 1-3 cases per 1000 subjects per year (Ashworth NL, 2011) Prevalence: 50 cases per 1000 subjects in the general population (Ashworth, NL 2011) More prevalent in women (9.2%) than men (.6%) Over 500, 000 surgeries annually “normal” pressures in compartment are 7-8 mm Hg, in CTS pressure rise above 30 mm Hg Leads to ischemia of median nerve PT implications??? Recap Charcot-Marie-Tooth Disease (CMT) – Most common inherited neuropathy – Peroneal nerve, followed by muscle of foot and leg – CMT-1 (schwann cells demyelination) – CMT-2 (ventral horns and DRG lumbar) – Slowly progressive, symmetric L/E weakness, atrophy, ↓ DTR, steppage gait, loss sensation L/E – Treatment- symptomatic, orthotics, skin care, ROM, prevent contracture, strengthening Carpal tunnel syndrome – Most common entrapment neuropathy – Pain, tingling, numbness, parasthesia, weakness – Median nerve compression, can lead to ischemia Compression and Entrapment syndromes Idiopathic Facial Paralysis (Bell’s Palsy) Unilateral involvement of CN VII Effects 20 per 100,000 each year Most common in age 20-40 years Compression and Entrapment syndromes Idiopathic Facial Paralysis (Bell’s Palsy) Cause unknown Viruses and cytokines believed to play a role Antibodies to herpes virus have been found in patients with Bell’s palsy Early symptoms include pain at mastoid process implicating an inflammatory process that causes demyelination Tumors can also compress CN VII More common with diabetes and pregnant women Compression and Entrapment syndromes Idiopathic Facial Paralysis (Bell’s Palsy) Clinical manifestations… – Unilateral facial paralysis develops rapidly – Asymmetrical facial appearance – Facial nerve innervates stapedius muscle (hearing abnormalities) – Facial nerve innervates autonomic fibers for taste, lacrimation, salivation which can also be affected Compression and Entrapment syndromes Idiopathic Facial Paralysis (Bell’s Palsy) Diagnosis… – Observe muscles of facial expression – EMG to test for degenerated nerve Compression and Entrapment syndromes Idiopathic Facial Paralysis (Bell’s Palsy) Treatment… – High dose steroids to prevent permanent damage – Antiviral medications including acyclovir may help – Clients treated within 3 days of paralysis: 100% recovery possible – Rate of recovery decreased to 84% by day 4 if not treated – Eye patch and artificial tears useful – Incomplete involvement usually recover completely over a course of weeks – PT implications???? mdchoice.com/photo/img/img0223.jpg Ulnar nerve Cubital tunnel syndrome Pisiform- Guyon’s canal  Thoracic outlet syndrome Scalene muscle Subclavian artery Brachial Plexus Adson’s Test Take deep breath and turn head to the affected side Recap Bell’s Palsy – Unilateral CNVII facial nerve – Etiology unknown- virus, antibodies to herpes virus – Unilateral facial paralysis – Dx-clinical, EMG – Tx-meds: steroids, antiviral, within 3 days onset, eye patch – PT implications Ulnar nerve palsy – Thoracic outlet syndrome – Adson’s Test Metabolic Neuropathies Diabetic neuropathy Progressive nerve fiber loss and atrophy Neural function deteriorates causing peripheral sensory & motor loss Usually occurs in a distal symmetric pattern Many subclinical forms depending on nerve(s) involved Caused by vascular changes, altered ATP synthesis, reduced concentrations of nerve growth factor We will discuss this further when we discuss metabolic syndromes!  Pathogenesis Hyperglycemia Microvascular injury (arteriosclerosis)  Vasoconstriction causes ↓blood flow to the area ↓amount of available blood to nerves resulting in ↓NCV and ischemia  Diabetes: Nerve damage (Neuropathy) movie Impaired nerve fiber mechanisms - – less neurotrophic factor to repair nerve damage Hyperglycemia Polyol Pathway-  nerve damage  Pathophysiology-Polyol Pathway High conc. of glucose (Hyperglycemia) will activate the enzyme aldose reductase, which converts glucose to Sorbitol Need to convert sorbitol to fructose because sorbitol causes osmotic stress (cell swell up) and cell damage, need to have enzyme sorbitol dehydrogenase for the conversion Some parts of the body that have very low levels of sorbitol dehydrogenase activity: – 1) retina of the eye-diabetic retinopathy – 2) kidney- diabetic nephropathy – 3) neuron- diabetic neuropathy Relationship of glycemic control and diabetes duration to diabetic retinopathy. Study with 1400 patients Retinopathy progression rate is related to HbA1c (simple blood test to identify plasma glucose concentration) Normal 6.5% Source: Diabetes Mellitus: Complications, Harrison's Principles of Internal Medicine, 19e Citation: Kasper D, Fauci A, Hauser S, Longo D, Jameson J, Loscalzo J. Harrison's Principles of Internal Medicine, 19e; 2015 Available at: http://accessmedicine.mhmedical.com/ViewLarge.aspx?figid=98732645&gbosContainerID=0&gbosid=0 Accessed: February 11, 2018 Copyright © 2018 McGraw-Hill Education. All rights reserved Infections and Inflammations Guillian Barré Syndrome – 1 to 2 cases per 100,000 persons – Characterized by flaccid paralysis and areflexia – Believed to be immune mediated disorder Influenza Epstein-Barr virus Cytomegalovirus Bacterial infections Following respiratory or GI illness common (eg Campylobacter jejuni) – Autoimmune theory believed to cause antibody-mediated demyelination (ie. Autoimmune attack of the myelin sheath) – Immunoglobulins are a safe and effective treatment – Most persons will recover but 20% can have permanent neurological deficits – PT implications???? Complex Regional Pain Syndrome Reflex Sympathetic Dystrophy (CRPS I) Can occur following 5% of all injuries Average age of CRPS is 30 years Injury at one somatic level initiates sympathetic efferent activity that affects multiple segmental levels. “reflex neurogenic inflammation” Diagnosis based upon clinical examination and history Complex Regional Pain Syndrome Recap Bell’s Palsy – Unilateral CNVII facial nerve – Etiology unknown- virus, antibodies to herpes virus – Unilateral facial paralysis – Dx-clinical, EMG – Tx-meds: steroids, antiviral, within 3 days onset, eye patch – PT implications Ulnar nerve palsy – Thoracic outlet syndrome – Adson’s Test Diabetic Neuropathy – Metabolic neuropathy, symmetrical loss sensory and motor functions – Microvascular injury, polyol pathway Guillain Barre Syndrome – Immne-related demyelination, flaccid paralysis and areflexia Complex Regional Pain Syndrome – Reflex sympathetic dystrophy