Neuro anatomy Chapter 8 (P327-335)
Disorders of Nerve, Neuromuscular Junction, and Muscle
 Disorders of PNS can be distinguished from CNS dysfunction by anatomical pattern of sensory or motor deficits
o Presence of lower motor neuron signs such as atrophy, fasciculations (involuntary muscle contraction),
decreased tone, or hyporeflexia suggest PNS dysfunction; paresthesias in peripheral nerve distribution
 Neuropathy – nerve disorder; site of pathology can be axons, myelin, or both; usually affect both sensory and
motor fibers in nerve, although one or other may be preferentially involved
o Mononeuropathy – focal neuropathy
o Mononeuropathy multiplex – multifocal neuropathy
o Polyneuropathy – generalized neuropathy
o Radiculopathy – neuropathy affecting spinal nerve roots
 Important causes of neuropathy include diabetes, mechanical causes, Lyme disease, HIV, CMV, varicella-zoster
virus, hepatitis B, toxins, malnutrition, immune disorders (Guillain-Barré syndrome), and hereditary
neuropathies (Charcot-Marie-Tooth disease)
 Diabetic neuropathy – produced by compromise of microvascular blood supply of peripheral nerves, o xidative
stress, autoimmunity, and neurotrophic and biochemical disturbance
o Most common is distal symmetrical polyneuropathy (glove and stocking pattern of sensory loss)
o Acute diabetic mononeuropathy can affect any cranial or spinal nerve; most common in CN III and
femoral and sciatic nerves; often partial or complete recovery over course of weeks to months
 Mechanical causes of nerve injury include extrinsic compression, traction, laceration, or entrapment by intrinsic
structurs
o Neurapraxia – temporary impairment of nerve conduction that usually resolves in hours to weeks
o Wallerian degeneration – degeneration of axons and myelin distal to site of injury
 As long as structural elements of nerve intact, axonal regeneration may occur at 1 mm/day
o Complex regional pain syndrome type 1 – reflex sympathetic dystrophy; follows injury without specific
nerve damage
o Complex regional pain syndrome type 2 – causalgia; follows damage to specific nerve
o Both types of complex regional pain syndrome characterized by intense local burning pain accompanied
by edema, sweating, and changes in skin blood supply
 In some situations when peripheral nerves severed or otherwise disrupted, they can be reanastomosed
surgically; some entrapment syndromes amenable to surgical decompression
 Painful paresthesias associated with neuropathies treated with anticonvulsants, serotonin-norepinephrine
reuptake inhibitors, or tricyclic antidepressants
 Guillain-Barré syndrome – acute inflammatory demyelinating polyneuropathy (AIDP); caused by immunemediated demyelination of peripheral nerves
o Onset typically occurs 1-2 weeks following viral illness, Campylobacter jejuni enteritis, HIV infection
o Presents with progressive weakness, areflexia, and tingling paresthesias of hands and feet
o Motor involvement typically much more severe than sensory
o Symptoms at worst 1-3 weeks after onset; recovery occurs over many months
o Diagnosis based on CSF demonstrating elevated protein without significantly elevated WBC
o EMG/nerve conduction studies compatible with demyelination
o Recovery occurs more quickly when patients treated with plasmapheresis or IV immunoglobulin therapy
o In severe cases, patients require intubation and mechanical ventilation
o Autonomic dysfunction can be prominent in some cases
o With care and immune therapy, majority of patients get complete or near-complete recovery
 Impaired neuromuscular transmission can lead to motor weakness without sensory deficits
 Myasthenia gravis – immune-mediated disorder in which there are circulating antibodies against postsynaptic
nicotinic acetylcholine receptors at neuromuscular junction of skeletal muscle cells
o Sometimes accompanied by other autoimmune phenomena
o Onset in 10s-20s more common in women; onset in 50s-60s more common in men
o Clinical features include generalized symmetrical weakness, especially of proximal limb muscles, neck
muscles, diaphragm, and eye muscles
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Involvement of bulbar muscles can cause facial weakness, nasal-sounding voice, and dysphagia
Reflexes and sensory exam normal
Weakness becomes more severe with repeated use of muscle or during course of day
15% of cases involve only extraocular muscles and eyelids (ocular myasthenia)
Ice pack test – placing bag of ice on closed eyelids for 2 minutes and reevaluating for improvement of
ptosis (reduced cholinesterase function at lower temperatures)
o Can also check clinical response to intermediate-acting acetylcholinesterase inhibitors (neostigmine)
o Anti-acetylcholine receptor antibodies (AchR-Ab) positive in 85% of cases of generalized myasthenia and
50% of cases of ocular myasthenia
o Half of patients with generalized myasthenia who are AchR-Ab negative have positive serology for
MuSK-Ab
o 12% of patients with myasthenia have thymoma, and many others have thymic hyperplasia
o Treated by immune therapy (anticholinesterase medications); titrate and monitor doses because excess
anticholinesterase can worsen weakness
 Pyridostigmine – long-acting cholinesterase inhibitor
o Many treated with thymectomy (whether thymus problems present or not); for patients under 60
 Should be performed when patients relatively clinically stable to minimize complications
o Short-term immunotherapy with plasmapheresis or IVIg can be helpful, particularly when patients in
myasthenic crisis requiring intubation, experiencing severe worsening symptoms, or in preparation for
elective surgery
o Longer-term immunosuppressive agents (steroids, azathioprine, mycophenolate, cyclosporine) help
 Myopathies – muscle disorders that produce weakness typically more severe proximally than distally without
loss of sensation or reflexes
o Common causes include thyroid disease, malnutrition, toxins, viral infections, dermatomyositis,
polymyositis, and muscular dystrophy
 Dermatomyositis and polymyositis – immune-mediated inflammatory myopathies; CPK elevated
o EMG (electromyography) studies compatible with myopathy
o In dermatomyositis, characteristic violet-colored skin rash, typically involving extensor surface of
knuckles and other joints
 Duchenne muscular dystrophy – most common form of muscular dystrophy; X-linked inheritance
Back Pain
 Musculoskeletal causes are most common; in individuals with onset over age 50, suspect neoplasm
 Back pain in younger person that worsens with exertion and improves with rest usually caused by
musculoskeletal problem like disc herniation
 Rule out radiculopathy
 Never forget to evaluate bladder, bowel, and sexual function in patients with back pain so irreversible loss of
function can be prevented
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Spondylolysis – fractures that appear in interarticular portion of vertebral bone between facet joints
Spondylolysthesis – displacement of vertebral body relative to vertebral body beneath it
o Anterolisthesis is anterior displacement; retrolisthesis is posterior displacement
o Anterolisthesis often coexists with spondylolysis
 Osteophytes – bony spurs that form on regions of apposition between adjacent vertebrae because of chronic
degeneration
Radiculopathy
 Radiculopathy – sensory or motor dysfunction because of nerve root pathology
o Often associated with burning, tingling pain that radiates or shoots down limb in dermatome of
affected nerve root
o May be loss of reflexes and motor strength in radicular distribution
 Chronic radiculopathy can result in atrophy and fasciculations
 Sensation may be diminished fi single dermatome involved, but sensation not usually absent because of overlap
of adjacent dermatomes; testing with pinprick more sensitive than touch
 Mild or recent-onset radiculopathy can cause sensory changes without motor deficits
 T1 radiculopathy can interrupt SNS pathway to cervical sympathetic ganglia, resulting in Horner’s syndrome
 Most common cause of radiculopathy is disc herniation; common in C6, C7, L5, and S1 nerve roots
 Straight-leg raise test helpful in diagnosis of mechanical nerve root compression in lumbosacral region; provides
traction on nerve roots
 Crossed straight-leg raising test – elevating asymptomatic leg causes typical symptoms in symptomatic leg
 Radicular symptoms may be increased by Valsalva maneuver
 Cervical radiculopathy – symptoms increased by flexing or turning head toward affected side
 Pain on percussion of spine may indicate metastatic disease, epidural abscess, osteomyelitis, or other disorders
of vertebral bones (not absolutely specific or diagnostic)
 Incidental disc bulges and other degenerative changes of spine common findings in asymptomatic individuals
 Lumbar stenosis – may result in neurogenic claudication (bilateral leg pains and weakness during walking)
 Diabetic neuropathy can involve nerve roots, particularly at thoracic levels, producing abdominal pain
 Epidural metastases most commonly occur in vertebral bodies, but can extend laterally to compress nerve roots
o Spread of cancer cells within CSF can involve nerve roots
 Guillain-Barré syndrome has predilection for nerve roots
 Reactivation of latent varicella-zoster virus (chickenpox) in DRG produces painful blistering lesions of herpes
zoster or shingles; occurs in dermatomal distribution and associated with sensory loss (less commonly motor)
o Herpes zoster most common in thoracic dermatomes but can occur anywhere
o Treatment with oral antiviral can shorten duration of blistering lesions
o Postherpetic neuralgia – severe pain that can persist after blistering eruption; shortened by treatment
with antiviral medications
o When herpes zoster occurs in CN V1, it can threaten vision, so prompt treatment critical
 Lyme disease – spirochete borne by ticks; can cause radiculopathies
 CMV polyradiculopathy seen in patients with HIV infection, most commonly in lumbosacral roots
o Milder form of radiculopathy caused by HIV itself
 Dumbbell-shaped nerve sheath tumors (schwannomas and neurofibromas) can occur in neural foramen,
producing radiculopathy; neurofibromatosis – presence of neurofibromas
Cauda Equina Syndrome
 Cauda equina syndrome – impaired function of multiple nerve roots below L1 or L2
 If deficits begin at S2 roots and below, there may be no obvious leg weakness
 Involvement of S2-S4 can produce distended atonic bladder with urinary retention or overflow incontinence,
constipation, decreased rectal tone, fecal incontinence, and loss of erections
 Conus medullaris syndrome – similar deficits that occur as result of lesions in sacral segments of spinal cord
 Causes of cauda equina syndrome include compression by central disc herniation, epidural metastases,
schwannoma, meningioma, neoplastic meningitis, trauma, epidural abscess, arachnoiditis, and CMV
polyradiculitis
Common Surgical Approaches to the Spine
 Indications for urgent surgery include rare instances where cord compression or cauda equina syndrome occurs
 Semiurgent surgery indicated in patients with progressive or severe motor deficits or occasional patient with
intolerable, medically intractable pain
 Elective surgery contemplated when clear radiculopathy present and conservative measures have been tried for
1-3 months but were ineffective
 Posterior approach with laminectomy (removal of lamina over affected levels); combined with discectomy to
remove herniated disc materla
o Posterior approach for foraminotomy to widen lateral recess thorugh which nerve root passes just
before it exits intervertebral foramen
o Preferred approach in lumbar spine
 Anterior approach can be used in C-spine; provides direct access to discs without traversing spinal canal and
allows mechanical fusion of adjacent vertebral bodies, usually using bone graft
o Favored in cases of thoracic disc herniation