Motor Neuron Diseases Flashcards Preview

Neuro 2 > Motor Neuron Diseases > Flashcards

Flashcards in Motor Neuron Diseases Deck (45)
Loading flashcards...

What is affected in Motor Neuron Diseases

-motor neurons, their motor axons, and secondarily the muscle fibers they innervated (the motor unit)



Infantile Spinal Muscular Atrophy
-autosomal recessive
-hypotonicity, hyporeflexia, fatal
-tongue fasciculations
-poor suck reflex
-abdominal respirations
Anterior Horn Cell Disease
-difficulty breathing, swallowing , die early from respiratory failure, "frog-leg" posture



-Juvenile Proximal Chronic Spinal Muscular Atrophy
-Autosomal recessive
-slowly progressive, fasciculations, proximal weakness, resembles myopathy
Anterior Horn Cell Disease
-atrophy of pectoralis & thigh muscles


Adult Onset Spinal Muscular Atrophy

-sproadic (some familial)
-Proximal, distal weakness
-hypotonicity, hyporeflexia
Anterior Horn Cell Disease


Werdnig-Hoffman Disease Tests

-EMG: signs of denervation and fasciculations
-Muscle Biopsy: group fiber atrophy
-Mutation: 'survival motor neuron gene' on chromosome 5q


Wolfart-Kugelberg-Welander Tests

-EMG & Biopsy: denervation changes
-Serum CK: normal
-Mutation: 'survival motor neuron gene' SNM1 is absent and the size of SMN2 determines if the patients have neonatal or juvenile form
-SMN2 is larger


Progressive Bulbar Palsy

Adult motor neuron disorders
-sproadic, fasciculations, Bulbar muscles weakness, rapidly progressive, tongue atrophy
-may develop ALS


Amyotrophic Lateral Sclerosis (ALS)

Adult motor neuron disorders
-mostly sporadic, some familial cases - 10%, hyperreflexia, spasticity
-muscle atrophy (fasciculations) , fasciculations, tongue atrophy, rapidly progressive (lethal)
-upper & lower motor neurons, bulbar weakness
-normal sensation

Presentation: difficulty swallowing & breathing
Late: biateral Babinski signs, hard to close mouth


Progressive Lateral Sclerosis

-sporadic, involves only upper motor neurons, spasticity
-hyperreflexia, more benign course
-little atrophy or signs of denervation


Progressive Spinal Muscular Atrophy

-mostly sporadic, progressive weakness, muscle atrophy, fasciculations, areflexia


Signs, Symptoms, & Labs of Motor Neuron Diseases

-Symmetrical or asymmetrical weakness
-inc. or dec. reflexes dep. on corticospinal tract involvement (ALS)
-normal sensation
-normal nerve conduction velocities
-denervation on EMG
-dec. # of motor units
-muscle biopsy shows atrophic fibers & fiber grouping


Cervical Spondylosis

-seen in MRI
-present: lower motor neuron signs in upper extremities secondary to nerve root compression & upper motor neuron signs in the lower extremities secondary to compression of spinal cord & corticospinal tracts


Kennedy's Disease

-Bulbo-spinal muscular atrophy
-more benign than ALS, family history
-mutations of the androgen receptor on the x chromosome
-Phenotype: gyneocomastia & testicular atrophy, lower motor neuron syndrome (atrophy, fasciculations, signs of denervation in limbs & tongue, mild neuropathy)
-serum CPK elevated
-DNA testing diagnostic


Pathology of ALS

-degeneration of the corticospinal tracts (lack of myelin)
-Bunina body: dense granules inclusion in cell body cytoplasm (ubiquitin accumulations)


Etiology of ALS

-unknown, some familial cases (genetic)


Possible etiologies of ALS and other motor neuron diseases

Genetic Defects
-SOD gene mutations in chromosome 21 in AD familial ALS
-Juvenile ALS: chromosome 2q33 (also 9q34, 15q15, 8q21), and also ALS associated with mutation of 9q21, XP
-ALS associated with other diseases such as chromosome 17-linked fronto-temporal dementia (FTD)
-an expanded section of DNA on chromosome 9 in the gene C90RF72 is most common cause of familial ALS with or without FTD
-Excitotoxicity: evidence suggests an inc. of glutamate mediated excitotoxicity causing neuronal degeneration (secondary)


Treatment of ALS

-Glutamate antagonists (riluzole)
-Experimental: creatine & antioxidants such as carotene, coenzyme Q10, vitamins C & E could be of benefit, COX 2 inhibitors, nerve growth factors
-physical therapy
-symptomatic treatments such as anticholinergics for sialorrhea, stool softeners, antispastic drugs, botulinum toxin
-respiratory assistance


Brachial plexus

-extends from spinal cord to distal aspect of axilla
-6 divisions, behind clavicle


Sensory Domain

-the skin region innervated by the sensory nerve fibers contained with a nerve root
-Dermatome: sensory domain of a root


Muscle Domain

-the muscles innervated by the motor nerve fibers contained within a nerve root
-Myotome: motor domain of a root


What are the 2 most common causes of radiculopathies?

1. Disk herniation & degeneration (>C6
-Spondylosis: C5 & C6> frequent
by age 60 yrs, 70% W and 85% M
after age 70 yrs, 93% W and 97% M

2. Lumbosacral radiculopathies
->95% of HNPs affect either L5 or S1


Clinical features of Radiculopathies?

-Pain (hallmark): sharp, stabbing, hot; electric, radiating, aggravated by maneuvers that stretch the root (cervical: neck extension, neck rotation, Spurling's maneuver)
-lower extremity (SLR used with L5 or S1 nerve root involvement is suspected and reverse SLR w/L4

-weakness & atrophy (motor nerve fibers, myotomal distrubution (muscle domain of root))
-Paresthesias & sensory loss: sensory nerve fibers, dermatomal distribution (sensory domain of a root)
-Muscle stretch reflexes (diminished or absent)

-Irritation = tingling



>50 yrs
-Cervical spondylosis: myeloradiculopathy (spinal canal stenosis)
-Lumbosacral spondylosis: neurogenic cladication (ambulation to LE pain & weakness), cauda equina syndrome


Radiculopathy: Fracture of Dislocation

-Trauma: major cause in young patients
minor cause amoung elderly
-Bone disease: osteoporosis; osteomalacia; Paget disease, Corticosteroid therapy, congenital anomalies


Radiculopathy: Infection

-immunosuppressed status
-Spinal surgery
-penetrating wound


Radiculopathy: Neoplasm

-history of cancer
-constitutional symptoms (weight loss)
-pain at rest
-neurologic deficit (cauda equina localization)


Evaluation of Radiculopathy

-H&P (most important):
Spinal cord compression: sensory level, anal tone, fecal or urinary incontinence, check cutaneous reflexes (abdominal; bulbocavernousus; anal wink; cremaster)
-Plain radiographs
-CT (+/- myelography)
-MRI: superior to CT for all spine conditions
greater contrast sensitivity (tumor & infection)
Non-ionizing radiation
Gadolinium contrast (scar tissue vs. recurrent disk protrusion)


EDX Testing

-yields physiologic info
-complements MRI (anatomic changes, high false+)
-False + studies extremely uncommon

-assesses sensory & motor nerve fibers
-assesses muscle fibers
-identifies demyelination & axon loss
-localized the disorder
-generates ddx or the actual diagnosis
-determines severity
-determines prognosis
-dictates management & follow-up


Radiculopathy: Conservative Treatment

-most w/acute radiculopathies improve in 6 weeks
-bed rest 0-2 days
-physical therapy (heat, cold, ultrasound, massage, stretching, ergonomic education)
-Meds: NSAIDS, prednisone, benzodiazephines
-Nerve Block


Radiculopathy: Surgical Treatment

-Etiology (neoplastic process)
-spinal instability
-severe or progressive weakness
-spinal cord compression
-cauda equina syndrome
-sphincter or sexual dysfunction
-incapacitating neurogenic claudication
-intractable pain (ill-advised if isolated pain with negative imaging)