Skeletal Muscle and PNS

Question 1

Trichinosis

Answer 1

• Trichinella spiralis (nematode) from pigs/pork
• Dystrophic calcification in muscle
• Muscle pain, periorbital edema, splinter hemorrhages; possible myocarditis or encephalitis

Question 2

Myotonic dystrophy

Answer 2

• Autosomal dominant
• Trinucleotide repeat disorder
• Facial muscle weakness, percussion and grip myotonia (can’t relax muscles), cardiac conduction defects
• Frontal balding, testicular atrophy, glucose intolerance
• Increased serum CK
• Causes of death: muscle wasting, cardiac fxn defects

Question 3

Amyotrophic lateral sclerosis

Answer 3

• Loss of upper and lower motor neurons (no sensory change)
• 40-60 yrs old
• Bad superoxide dismutase 1
• Begins as muscle wasting in one hand, fasciculations
• Spasticity, Babinski sign, muscle weakness, respiratory muscle paralysis

Question 4

Acute intermittent porphyria

Answer 4

• Autosomal dominant
• Uroporphyrinogen synthase deficiency —> increased PBG and ALA
• Urine wine-red on exposure to light
• Increasing p450 (e.g. with alcohol) precipitates attacks
• Recurrent severe abd pain, peripheral neuropathy, psychosis, dementia

Question 5

Vitamin B12 deficiency

Answer 5

• Posterior column and lateral corticospinal tract demyelination
• Dementia, peripheral neuropathy

Question 6

Charcot-Marie-Tooth disease

Answer 6

• Autosomal dominant
• Peroneal nerve neuropathy
• Lower BLE muscle atrophy; “inverted bottle” appearance of legs

Question 7

Guillain-Barré syndrome

Answer 7

• Autoimmune demyelination syndrome
• Common preceding infections: viruses, M. pneumoniae, Campylobacter jejuni
• Rapidly progressive ascending motor weakness starting in proximal muscles
• Depressed/absent DTRs
• Glove and stocking paresthesias
• Increased CSF proteins

Question 8

Ulnar nerve injury (C8-T1)

Answer 8

• Medial epicondyle Fx
• “Claw hand”

Question 9

Radial nerve injury (C5-T1)

Answer 9

• Midshaft humerus Fx or “Sunday morning palsy”
• Wrist drop

Question 10

Axillary nerve injury (C5-6)

Answer 10

• Surgical neck of humerus Fx, anterior shoulder dislocation
• Can’t abduct arm or hold horizontal position with downward force applied

Question 11

Median nerve injury (C6-T1)

Answer 11

• Median nerve entrapment; RA, pregnancy, overuse
• Sensory abnormalities in 1st 3 fingers; may have “ape hand” with thenar atrophy

Question 12

Common peroneal nerve injury (L4-S2)

Answer 12

• Lead poisoning, fibula neck Fx, cast tightness
• Loss of foot eversion/dorsiflexion, toe extension
• “Slapping gait” or “high-stepping gait”
• Plantar flexion with foot drop and inversion
• Loss of ankle jerk reflex
• Sensory deficits on anterolateral leg and dorsal foot

Question 13

Erb-Duchenne palsy

Answer 13

• Brachial plexus lesion at C5-6
• “Waiter’s tip” deformity

Question 14

Duchenne and Becker muscular dystrophies

Answer 14

• Progressive muscle degeneration, esp. in pelvic and shoulder girdles
• XLR
• Decreased dystrophin on muscle biopsy, very high CK

Question 15

Central core disease

Answer 15

• Autosomal dominant
• Ambulatory but weaker than normal; decreased DTRs
• Predominance of type I fibers
• Risk for malignant hyperthermia triggered by some anesthetics

Question 16

Rod myopathy

Answer 16

• Rod-like inclusions accumulate w/in sarcoplasm
• Hypotonia, delayed motor development, kyphoscoliosis, involvement of face/pharynx/neck

Question 17

Central nuclear myopathy

Answer 17

• Skeletal muscles w/ centrally located nuclei
• Facial muscle involvement w/ ptosis
• Dynamin 2 gene
• Type I fiber predominance

Question 18

Polymyosotis

Answer 18

• Patients >20 yrs
• CD8 T cell autoimmune
• Proximal muscle weakness, dysphagia, difficulty holding head up

Question 19

Inclusion body myositis

Answer 19

• Patients >50 yrs
• CD8 T cells
• Beta-amyloid inclusions (Congo red)
• Proximal OR distal muscle weakness, dysphagia

Question 20

Dermatomyositis

Answer 20

• Rash on upper eyelids, face, trunk
• CD4 and CD8 T cells, immune complexes

Question 21

Glycogen storage diseases

Answer 21

• Pompe disease: acid maltase deficiency, hypotonia, death <2 yrs
• McArdle disease: myophosphorylase deficiency, muscle cramps w/ exercise
• Tarui disease: PFK deficiency, muscle cramps w/ exercise

Question 22

Lipid myopathies

Answer 22

• Carnitine deficiency: lipids in sarcoplasm, proximal muscle weakness + atrophy
• Carnitine palmitoyltransferase deficiency: muscle pain after exercise or fasting

Question 23

Mitochondrial disease

Answer 23

• Accumulation of mitochondria —> ragged red fibers
• Cytochrome oxidase deficiency

Question 24

Spinal muscular atrophy

Answer 24

• Autosomal recessive denervation disease
• Infantile (Werdnig-Hoffman): fatal w/in 1 yr, loss-of-fxn in apoptosis inhibitor gene
• Juvenile (Kugelberger-Welander): limb-girdle dystrophy; not necessarily progressive

Question 25

Morton neuroma

Answer 25

• Swelling of plantar interdigital nerve b/w 2nd, 3rd, or 4th metatarsals
• Repeated nerve compression from wearing high heels

Question 26

Spinal and peripheral schwannomas

Answer 26

• Often from dorsal (sensory) spinal roots with radicular pain and SC compression
• Peripheral schwannomas: head, neck, extremities
• Firm and tan/gray w/ hemorrhae, necrosis, xanthomatous change, cystic degeneration; may have Verocay bodies

Question 27

Encephalomyoneuritis

Answer 27

• Paraneoplastic syndrome
• Sensory changes, gait change, confusion, weakness
• Small-cell lung cancer w/ anti-Hu Abs

Question 28

Opsonus-myoclonus

Answer 28

• Children: neuroblastoma
• Adults: 10% of CA, often Hodgkin lymphoma

Question 29

Eaton-Lambert syndrome (myasthenic-myopathic syndrome)

Answer 29

• Paraneoplastic syndrome often associated w/ small-cell lung CA
• Defect in Ach release from IgG targeting