B6.086 Statin Myopathy

Question 1

normal muscle histo

Answer 1

polygonal fibers, same sized
very little intervening stroma
clear, no infiltrates
cut in a cross section

Question 2

concerning findings in a presentation of myopathy

Answer 2

severe cramps
brown urine
flank pain

Question 3

common potential causes of myopathy

Answer 3

statin use
steroid use
overuse injury
alcohol use

Question 4

what to do if statin myopathy doesn’t terminate months after cessation of statin

Answer 4

get a muscle biopsy to investigate

Question 5

how to test for enzyme activity in a muscle biopsy

Answer 5

dark brown = intact enzyme activity

light = not functional muscle

Question 6

potential causes of a completely light enzyme study

Answer 6

complete lack of staining due to technical issues
complete lack of staining due to enzyme lack
completely normal (could be staining for an abnormal protein that is supposed to be absent)

Question 7

what is McArdle disease

Answer 7

mycophosphorylase deficiency (GSD type V)
most common GSD affecting muscle
glycogen is not properly broken down in muscle cells

Question 8

typical presentation of McArdle

Answer 8

typically present in adolescence or early adulthood with exercise intolerance, fatigue, myalgia, cramps, poor endurance, muscle swelling, and fixed weakness
resting elevations in CK and episodes of rhabdo
higher prevalence in Spanish population

Question 9

management of McArdles

Answer 9

avoidance of low carb diets and low to moderate aerobic exercise

Question 10

useful lab tests in evaluating severe muscle pain and dark urine

Answer 10

CBC
CK
creatinine
urinalysis

Question 11

muscle biopsy findings in necrotizing myopathy

Answer 11

necrotic muscle fibers are eosinophilic and lack striation (very pink and lose internal features due to death)
macrophages present to clean up damaged fibers

Question 12

cerivastatin

Answer 12

old statin drug withdrawn from market due to high incidence of rhabdo
likely due to high lipophilicity and bioavailability

Question 13

how is lipophilicity related to statin myopathy

Answer 13

more lipophilic = more statin integrates into muscle cell membrane = more muscle damage

Question 14

symptoms of rhabdo

Answer 14

fluid and electrolyte abnormalities
cardiac dysrhythmias
cardiac arrest from severe hyperkalemia
acute kidney injury
compartment syndrome
DIC

Question 15

association of acute kidney injury and rhabdo

Answer 15

common complication
15-50% frequency
risk is lower in patients with CK levels at admission less than 15-20,000 units/L

Question 16

how does rhabdo cause hyperkalemia

Answer 16

necrosis causes K to spill into bloodstream

Question 17

what is muscle typing

Answer 17

staining muscle fibers with ATP 4.6 and ATP 9.4
type 1 fibers are light
type 2 fibers are dark
helpful in looking for patterns of myopathies

Question 18

causes of type 2 fiber atrophy

Answer 18

most common: steroids
alcoholism
Cushings
thyroid disease
*not typical of statin induced*

Question 19

features of neurogenic muscle damage

Answer 19

type 1 and type 2 fiber atrophy

Question 20

alcoholic myopathy

Answer 20

most common neuromuscular disorder
damages muscle membranes via acetaldehyde and free radicals
can induce necrosis and rhabdo
most common myotoxic effect is type 2 atrophy

Question 21

other disease unmasked by statins

Answer 21

hypothyroidism
hypovitaminosis D
acute or chronic renal failure
obstructive liver disease