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primary demyelination

Schwann cell dysfunction due to direct injury to the Schwann cell or myelin sheath

secondary demyelination

Schwann cell dysfunction due to underlying axonal abnormalities

signs of remyelination process

shortened intermodal lengths, accumulation of supernumerary Schwann cells around axons (onion bulbs) and nerve enlargement (hypertrophic neuropathy)

most common cause of peripheral neuropathy in the US

diabetes mellitis

most common type of neuropathy

axonal neuropathy (specifically distal axonal neuropathy)

how to differentiate between axonal and demyelinating neuropathies

electrophysiologic studies; nerve conduction velocity is near normal in axonal, but decreased in demyelinating

major clinical manifestations of peripheral neuropathy

muscle weakness, muscle atrophy, sensory loss, paresthesia, pain, and autonomic dysfunction

most common form of diabetic neuropathy

distal, predominantly sensory, polyneuropathy (predominantly axonal with some demyelination)

uremic neuropathy

distal sensorimotor axonal polyneuropathy secondary to chronic renal failure; usually stabilizes; predominantly axonal degeneration of large-diameter fibers

critical illness polyneuropathy

associated with sepsis and multiorgan failure; axonal and predominantly motor; may occur when trying to wean off ventilator support and is associated with myopathy

alcoholic neuropathy

distal sensorimotor axonal polyneuropathy (dying back type); may be nutritional or direct toxicity from ethanol

nutritional neuropathy is (axonal/ demyelinating)


Guillain-Barre Syndrome

acute symmetric neuromuscular paralysis that often begins distally and ascends proximally (most commonly caused by AIDP)


acquired, immune-mediated neuropathy that often follows bacterial, viral, or mycoplasmal infections (which present as antecedent infections)

Fisher Syndrome

constellation of symptoms that complicates 5% of Guillain-Barre cases; includes opthalmoplegia, ataxia, and areflexia

complications and resolution of Guillain-Barre

usually resolves in 2-4 weeks; can cause cardiac arrhythmias, hypotension or HTN; increased protein in CSF

two common nerve sheath tumors

schwannoma and neurofibroma


benign, slow-growing, typically encapsulated neoplasms that original in cranial nerves, spinal roots, or peripheral nerves; adults; rarely become malignant

vestibular/acoustic schwannoma

arise from vestibular branch of 8th cranial nerve; cause sensorineural hearing loss, tinnitus, and vestibular dysfunction

complications of vestibular schwannoma

enlarge the meatus and extend medially into subarachnoid space of cerebellopontine angle, compressing 5th and 7th nerves, brainstem, and cerebellum; may cause increase ICP, hydrocephalus, and tonsillar herniation

defining feature of NF2 gene mutation

bilateral vestibular schwannomas

spinal schwannomas

intradural, extramedullary tumors that usually arise from sensory (dorsal) spinal roots, producting radicular pain and cord compression

pathology of schwannomas

oval and well demarcated with variable size; cut surface is firm, tan/gray, and can have focal hemorrhage, necrosis, cystic degeneration, xanthomatous change

histology of schwannomas

antoni A: eosinophilic cytoplasm, indistinct borders, and verocay bodies (nuclei palisade like flocks of birds), and antoni B: indistinct cytoplasm in loose, vacuolated background; degenerative changes common (foam cells, etc)


benign, slowly growing tumors of peripheral nerve, composed of Schwann cells, perineurial-like cells, and fibroblasts (Schwann cells are the neoplastic ones); potential for degeneration to malignant peripheral nerve sheath tumor; associated with NF1

pathology of neurofibromas

poorly circumscribed, fusiform enlargement with diffuse intrafascicular growth (may greatly enlarge fascicles, called plexiform neurofibroma)

cutaneous neurofibromas

originate from dermal nerves and cause soft nodular or pedunculated skin tumors

malignant peripheral nerve sheath tumor

poorly differentiated spindle cell sarcoma resulting in unencapsulated, fusiform enlargement of a peripheral nerve; adults and usually larger nerves; 50% in patients with NF1; increased risk from irradiation; prone to local recurrence and bloodborne mets

anterior horn cell disorders

wasting and weakness without sensory changes; EMG shows chronic partial denervation, abnormal spontaneous activity, and reduced voluntary control. Mild elevation of CK.

infantile spinal muscular atrophy (Werdnig-Hoffman)

AR genetic disorder, first 3 months of life. floppy baby, difficulty sucking, swallowing, ventilating. rapidly progressive -> death by age 3.

intermediate spinal muscular atrophy (chornic Werdnig-Hoffman)

AR genetic disorder begins in latter hald of 1st year. Wasting and weakness of extremities, slow progression to kyphoscoliosis and contractures. Survival is good.

juvenile spinal muscular atrophy (Kugelberg-Welander)

AR or sporadic genetic disorder presents in childhood or early adolescence with proximal limb weakness -> disability early in adult life.

polio virus infection

RNA virus spread fecal-oral. Prodromal phase of fever, myalgia, malaise, and URI/GI illness. Later develop asymmetric weakness or paralysis from involvement of anterior horn of lower motor neurons. Loss of tone and reflexes. PMN or lymphocytic pleocytosis in CSF. Mgmt is supportive.

postpolio syndrome

years after polio illness, increasing weakness that may be dye to loss of anterior horn cells with aging from an already decreased pool

West Nile

mosquitos -> meningoencephalitis or acute paralytic poliomyelitis. Paralytic form characterized by acute, asymmetric weakness or rapidly ascending quadriplegia. CSF PMN pleocytosis, viral IgM. Tx is supportive.

denervation atrophy of muscle is a sign of...

axonal degeneration

segmental demyelination

diseases affecting Schwann cell (dysfunction or damage); lead to loss of myelin which is replaced by shorter myelinated internodes -> thinly myelinated axons that look like "onion bulbs", can develop axonal injury

axonal degeneration

primary involvement of neuron and its axon (trauma, ischemia, neuronopathy, axonopathy); causes Wallerian degeneration, myelin ovoids. often followed by axonal regeneration and reinnervation of muscle. causes denervation atrophy of muscle.


primary abnormality of the muscle fiber itself

regenerating cluster

multiple closely aggregated, thinly myelinated small-caliber axons; evidence of nerve regeneration. accounts for some functional recovery after nerve injury.

Guillian-Barre (AIDP)

weakness beginning in distal limbs but rapidly advancing to affect proximal muscle function; associated with inflammation and demyelination of nerve roots and peripheral nerves

pathogenesis of GB

likely a T-cell immune-mediated response secondary to infection with campylobacter, Epstein-Barr, etc. Causes perivenular and endoneurial infiltration by lymphocytes, macrophages, and a few plasma cells, localizing to the spinal and cranial motor roots. CSF shows elevated protein but no pleocytosis (this is limited to the nerve root area).

clinical course of GB

ascending paralysis with early loss of deep tendon reflexes, slowed nerve conduction velocity, and hospitalization. tx = plasmapheresis.

chronic IDP

chronic symmetric mixed sensorimotor polyneuropathy that may occur instead of the traditional acute course seen with GB. remission induced with steroids and plasmapheresis.

VZV (shingles)

latent infection within neurons of sensory ganglia. reactivation common in thoracic or trigeminal distribution, leading to active infection of epidermal cells

hereditary motor and sensory neuropathy type 1 (Charcot-Marie-Tooth)

AD disorder presents in childhood or early adulthood with progressive muscular atrophy of the leg below the knee +/- problems of the foot. heterogeneous inheritance associated with mutations in PMP22, CX32, MPZ, PRX, and MBP (myelin-associated genes). morphology shows onion bulbs, enlargement of periph nerves, degeneration of posterior columns. normal life span.

diabetic peripheral neuropathy

distal symmetric sensorimotor neuropathy (think ulcers) +/- autonomic neuropathy (hypoTN) and sometimes focal asymmetric neuropathy (from ischemia or vascular insuff). assoc with polyol pathway and glycation of proteins.

pathology of diabetic neuropathy

axonal degeneration + some segmental demyelination. endoneurial arterioles are thickened and PAS+.

traumatic neuroma

mass of tangled axonal processes that develops after trauma to a nerve

compression neuropathy

carpal tunnel syndrome (women, bilateral). numbness and paresthesias in tips of thumb and first two digits. several others are also common.

Morton neuroma

histologic finding of chronic compression of interdigital nerve in the foot; occurs more common in women

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