PNS: Class 1 - Review

• Study notes based on the specified text:

Peripheral Nervous System Review

• The Peripheral Nervous System (PNS) encompasses neural structures outside the brain and spinal cord, acting as a link to the external environment.
• The PNS facilitates the reception of stimuli through afferent nerves and responses through efferent nerves.
• The PNS includes sensory receptors, peripheral nerves, associated ganglia, and efferent motor endings.
• Peripheral nerves are supported & covered by 3 connective tissue layers; from deep to superficial: Endoneurium, Perineurium, Epineurium
• Endoneurium surrounds each axon and is the innermost layer.
• Perineurium surrounds groups of neurons (fascicles) and is the middle layer.
• Epineurium surrounds the entire nerve and is the outermost layer.
• Myelinated nerves have an extra membrane for electrical insulation, leading to faster nerve impulse conduction.
• Unmyelinated nerves lack this extra membrane, resulting in slower conduction times.

Peripheral Nervous System Terminology

• Neuropathy refers to a functional disturbance or pathological change in nerve function.
• Neuralgia is pain along the distribution of nerves, usually without objective signs or structural damage.
• Neuritis indicates inflammation of a nerve.
• Neuroma is an overgrowth of nerve cells.
• Radiculitis is inflammation of a spinal nerve root.
• Radiculopathy involves compression of a nerve root, leading to numbness or weakness.
• Polyradiculopathy describes a condition affecting more than one nerve root.
• Plexopathy is a disorder involving one of the major neural plexuses.
• Fasciculation is the spontaneous contraction of muscle fibers in denervated tissue.
• Flaccidity is paralysis with a lack of muscle tone in the affected muscles, accompanied by decreased or absent tendon reflexes.
• Atrophy is the decrease in size or wasting away of a body part or tissue.
• Double Crush Syndrome involves nerve compression or injury in more than one location, such as median nerve compression at both the carpal tunnel and pronator teres.

Peripheral Neuropathy Types

• Peripheral nerves have motor, sensory, and autonomic functions, leading to different neuropathy presentations based on the affected nerve type.
• Motor Neuropathy results in weakness, flaccid paralysis, atrophy, and decreased reflexes.
• Sensory Neuropathy results in paresthesias, dysesthesias, pain, and numbness.
• Autonomic Neuropathy results in hypotension, anhidrosis or diaphoresis, and diarrhea or constipation.
• Mixed Neuropathy can present as a combination of any of motor, sensory, and autonomic.

Nerve Injuries

• Neuropraxia involves compression without structural damage, with intact endo, peri, and epineurium, resulting in mild weakness and full recovery.
• Transient-comes and goes after nerve compression which causes mild ischemia of the nerve fibre
• Axonotmesis involves axon damage while connective tissues remain intact, leading to Wallerian degeneration, paresis/paralysis, atrophy, and variable recovery.
• Often occurs after severe or prolonged compression.
• Neurotmesis is the complete severance of the axon, resulting in Wallerian degeneration, requiring surgical intervention, and leading to incomplete recovery.
• Often occurs after gunshot or stab wounds, avulsion injuries

Tissue, Muscle, Sensory and Prognosis in Nerve Injuries

• In Neuropraxia there is no tissue damage, only segmental demyelination and no degeneration, sensory issues include paresthesia and dysesthesia, with mild compression/traction as MOI.
• In Axonotmesis, axles are damaged with Wallerian degeneration, atrophy and sensory loss, with prolonged compression, with variable prognosis.
• In Neurotmesis, axons and connective tissue destroyed causing Wallerian degeneration and atrophy; sensory loos with a poor prognosis and a high chance of of surgery after Severance, rupture.

Nerve Regeneration

• Peripheral nerves can regenerate if the nerve cell body is intact.
• Intact endoneurial tubes, as in axonotmesis, provide a good pathway for nerve regeneration.
• Segmental demyelination occurs when compression causes myelin breakdown, exposing the axon.
• Schwann cells reproduce to form more myelin.

Wallerian Degeneration

• Wallerian Degeneration, also known as axonal degeneration, is the degeneration of an axon distal to a lesion site.
• After a nerve fiber is severed, the part distal to the injury degenerates.
• The segment between the nerve cell body and the injury site remains intact.
• The proximal and distal ends of the endoneurium are usually surgically attached for better outcomes.
• The axon continues to re-grow until it reaches a muscle or sensory receptor.

Causes of Peripheral Nerve Lesions

• Nerve lesions may result from internal and external compression like bony callus, tight muscles, tumors, edema/crutches, casts).
• They can also be from trauma, such as crush injuries, severance (knife, bullet), industrial accidents, birth trauma.
• Systemic disorders: leprosy, pregnancy, hypothyroidism, diabetes, kidney & heart conditions play a role.

Common Symptoms of Peripheral Nerve Lesions

• Edema occurs due to inflammation or as a result of damaged autonomic nerve fibers.
• Altered tissue health results from loss of autonomic function, trophic changes to skin, hair & nails)
• Altered motor function includes flaccid paralysis and muscle wasting, possible fibrillation within a few weeks.
• Characteristic holding patterns such as wrist drop or claw hand may be present.
• Contractures develop due to unopposed antagonist muscles.
• Scar tissue is present at the lesion site and can interfere with regeneration of the nerve.
• Compensatory changes such as tendonitis may occur.
• Diminished deep tendon reflexes occur.
• Pain may be accompanied with decreased or altered sensation interpreted as pain.

Recovery Phases

• Acute Phase: Focuses on healing and preventing complications, can involve immobilization like splinting or bracing, time dictated by MD
• Recovery Phase: Reinnervation occurs, emphasis on retraining and re-education.
• Motor retraining includes Being about to hold muscle in shortened position
• Desensitization includes stroking the skin with various textures, for sensory stimulation
• Discrimination sensory re-education identifies of objects with, then without, visual cues (stereognosis).
• Chronic Phase: Training compensatory function when recovery potential has peaked, might need splint or brace.

Muscle Weakness: Neurogenic vs Myogenic

• Neurogenic muscle weakness is caused by neuropathy, exhibits a distal-to-proximal distribution, fasciculations may be present, reflexes are diminished with sensory signs and symptoms.
• Myogenic muscle weakness is caused by myopathy, exhibits a proximal-to-distal distribution, fasciculations are absent, reflexes are often preserved and has no sensory signs.

Precautions & Treatment

• Avoid traction on regenerating nerves.
• Treat edema with elevation, nodal pumping, and draining techniques proximal to the edema.
• Apply segmental techniques proximal to the lesion at right angles to the regenerating nerve direction.
• Use blocking techniques with the ulnar border of the hand proximal to the lesion to prevent drag on the healing tissue.
• Delay work on the lesion site until regeneration has passed it (approximately 2 weeks post trauma or 3 weeks post surgery).
• Flaccid or weakened muscles distal to the lesion are treated with light strokes and gentle compressions.
• PROM can be used to shorten the affected tissue and nerve.

Nerve Compressions vs Nerve Injuries

• Treatment for nerve compression/entrapment (neuropraxia) differs greatly from nerve injuries (axonotmesis, neurotmesis).
• Non-degenerative conditions (neuropraxia) typically present with paresthesia, dysesthesia, pain, and mild weakness, indicating simple compressions or entrapments where the key is to relieve compression at the site.
• Examples include most cases of: Saturday night palsy, Crutch palsy, Supinator syndrome, Cubital tunnel compression, Guyon's canal compression, Pronator teres syndrome, Carpal tunnel syndrome, Piriformis syndrome, Thoracic outlet syndrome
• Degenerative conditions (axonotmesis, neurotmesis) present with atrophy, flaccidity, significant weakness/paralysis, and sensory loss, requiring extreme care and adherence to precautions for regenerating lesions.
• Examples include: Bell's palsy, Erb's paralysis, Klumpke's paralysis, Injury to any nerve serious enough to cause atrophy, flaccidity, significant weakness, paresis, paralysis, sensory loss.
• Present as the various deformities - ape hand, oath hand, benediction sign, claw hand, wrist drop, foot drop, calcaneovalgus, steppage gait, waiter's tip etc - we discuss

Assessment

• Palpation to assess muscle bulk/atrophy, sweating (anhidrosis/diaphoresis), edema, contractures, and tenderness (hyper/hypo/dysesthesia).
• ROM Testing to compare bilaterally, and includes both PROM, and AAROM.
• Myotome: assessment of motor neuron of nerve root, assessing the motor neuron from the root anterior root.
• Dermatomes: Area of skin nerve innervates (dorsal root).
• Deep Tendon Reflexes are tested, and will be negative with complete lesion, and diminished with a partial lesion (hyporeflexia).
• Hyperreflexia usually indicative of an upper motor neuron (CNS) lesion
• Sensory Testing identifies areas of dysfunction correlating to affected nerve function, and includes tests for deep and light touch, 2-point discrimination-dermatomes, testing for skin sensitivity.
• Includes testing for piloerector response, temperature.
• Vibration tests with tuning fork.
• Includes assessment of reactivity, clumsiness, balance issues.