B6.054 Steroid Myopathies

Question 1

symptoms of myopathy

Answer 1

difficulty climbing stairs. standing
falls
trouble combing hair, brushing teeth
dysphagia / dysarthria
fatigue, myalgia, tenderness

Question 2

signs of myopathy

Answer 2

proximal weakness: neck, shoulder, hip
normal tendon reflexes
normal sensory exam
facial or bulbar weakness

Question 3

Ddx for myopathy

Answer 3

myositis
MD
toxic exposure: SANAM
metabolic enzyme defect
mitochondrial muscle disease
endocrinopathy
critical illness myopathy

Question 4

Ddx for proximal muscle weakness

Answer 4

myopathy
NMJ defect (lambert eaton, MG)
CIDP (inflammation of peripheral nerves)
motor neuron diseases: SMA, ALS
myelopathy
sarcopenia

Question 5

when does muscle aging start?

Answer 5

age 40

Question 6

lab evaluation of myopathic disorders

Answer 6

serum CK
electrolytes, thyroid
serum Abs
needle EMG
nerve conduction study
biopsy
non-ischemic forearm test
urine for myoglobin
muscle imaging
molecular/genetic studies

Question 7

how might you get an excess of endogenous steroids

Answer 7

Cushings > bilateral adrenalectomy > excessive pituitary ACTH secretion > proximal myopathy (Nelson Syndrome)

Question 8

which steroids are particularly likely to cause drug induced steroid myopathy

Answer 8

9-a-fluorinated corticosteroids
triamcinolone, betamethasone, dexamethasone
(long duration)

Question 9

which steroids rarely cause myopathy

Answer 9

prednisone dose equivalent < 30 mg qd

Question 10

complications of critical illness

Answer 10

CIM: critical illness myopathy
CIN: critical illness neuropathy
PNMB: prolonged neuromuscular blockade

Question 11

mechanisms of steroid myopathy

Answer 11

not fully understood

likely due to impaired protein synthesis and muscle catabolism

Question 12

which muscle fibers are more susceptible to steroid myopathy

Answer 12

type 2 fibers (fast, glycolytic)

Question 13

cellular transcription changes caused by steroids that can induce myopathy

Answer 13

induced ubiquitin ligases: atrogin 1, muscle RING finger 1
suppress mammalian/ mechanistic target of rapamycin (mTOR)
these changes lead to an imbalance between anabolism and catabolism of muscle proteins, resulting in atrophy

Question 14

growth factor changes contributing to steroid myopathy

Answer 14

negative changes in IGF-1 and myostatin

Question 15

muscle weakness pattern associated with Cushings

Answer 15

insidious onset

proximal muscle weakness and wasting without involvement of distal or cranial muscles

Question 16

fat redistribution in Cushings

Answer 16

supraclavicular and temporal fossa
facial rounding
central obesity
buffalo hump

Question 17

skin findings in Cushings

Answer 17

wide (>1 cm) purple striae
bruising
hirsutism
poor wound healing

Question 18

pediatric findings in Cushings

Answer 18

decreased linear growth with continued weight gain

Question 19

behavioral / psych effects of Cushings

Answer 19

decreased libido
lethargy
depression

Question 20

other endocrine changes in Cushings

Answer 20

impaired glucose tolerance / diabetes

menstrual changes

Question 21

muscle weakness seen in exogenous steroid myopathy

Answer 21

proximal, symmetric weakness
legs > arms
wasting and myalgias

Question 22

systemic effects of exogenous steroids

Answer 22

weight gain
HTN
hyperlipidemia
glucose intolerance
diabetes
osteopenia
menstrual changes
impotence

Question 23

purpose of EMG

Answer 23

measure integrity of nerves, muscles, and their junction

Question 24

what makes up a normal motor unit action potential

Answer 24

1 axon with its constituent muscle fibers

Question 25

appearance of nerve injury on EMG

Answer 25

more fiber recruitment extra amplification polyphasic shape rather than triphasic

Question 26

appearance of muscle injury on EMG

Answer 26

action potential amplitude decreased, but shape is the same

Question 27

lab results seen in steroid myopathy

Answer 27

normal CK | normal or mild myopathy on EMG

Question 28

muscle pathology of steroid myopathy

Answer 28

type 2 fiber atrophy | myosin loss

Question 29

treatment of endogenous steroid myopathy

Answer 29

pituitary tumor removal in Cushings | ketoconazole

Question 30

treatment of exogenous steroid myopathy

Answer 30

reduce dose of steroids | supportive care / physical therapy

Question 31

mnemonic for generalized weakness in the ICU

Answer 31

``` MUCESS Medication (steroids, NMBA) Undiagnosed neuromuscular disorders (ALS, MG) Critical illness myopathy / neuropathy Electrolyte disorders Systemic illness Spinal cord damage ```

Question 32

what is Guillain-Barre

Answer 32

ascending paralysis, often post infectious (GI or resp) | peripheral neuropathy and weakness that eventually progresses to resp failure

Question 33

what is an example of a trigger of Guillain-Barre

Answer 33

vaccines (flu shots) | 1/100,000

Question 34

causes of muscle weakness after ICU admit

Answer 34

``` CIM CIP prolonged NM blockage acute necrotizing myopathy cachectic myopathy not GBS ```

Question 35

medical conditions associated with CIM

Answer 35

``` sepsis renal/liver failure asthma organ transplant use of IV steroids and/or NMBAs ```

Question 36

challenges associated with NM evaluation in the ICU

Answer 36

history and exam may be unobtainable or unreliable due to sedation, intubation, or encephalopathy reflexes may be preserved even in patients with severe myopathies/neuropathies muscle atrophy may be difficult to detect due to generalized edema

Question 37

useful investigations in evaluating ICU weakness

Answer 37

``` MRI cervical spine, and possibly brain nerve conduction repetitive nerve stimulation studies for PNMB needle electromyography serum CK, ANA, RF, TSH, aldolase CSF if suspecting GBS ```

Question 38

how many pts get CIM?

Answer 38

up to 46% of patients evaluated for ICU weakness

Question 39

clinical features of CIM

Answer 39

severe resp weakness requiring ventilator generalized or proximal flaccid paralysis muscle atrophy cranial nerves usually spared normal sensory exam reflexes may be normal, reduced, or absent

Question 40

lab features of CIM

Answer 40

CK often mildly elevated within 9 days after exposure to steroids, but can remain normal or very low aldolase may be elevated

Question 41

which types of sensory nerves are tested by nerve conduction studies

Answer 41

a-alpha a-beta larger and faster conduction velocity proprioception and touch sensing

Question 42

which types of sensory nerves are ignored by nerve conduction studies

Answer 42

a-delta C smaller and slower conducting pain and temperature sensing