B6.054 Steroid Myopathies Flashcards
symptoms of myopathy
difficulty climbing stairs. standing falls trouble combing hair, brushing teeth dysphagia / dysarthria fatigue, myalgia, tenderness
signs of myopathy
proximal weakness: neck, shoulder, hip
normal tendon reflexes
normal sensory exam
facial or bulbar weakness
Ddx for myopathy
myositis MD toxic exposure: SANAM metabolic enzyme defect mitochondrial muscle disease endocrinopathy critical illness myopathy
Ddx for proximal muscle weakness
myopathy NMJ defect (lambert eaton, MG) CIDP (inflammation of peripheral nerves) motor neuron diseases: SMA, ALS myelopathy sarcopenia
when does muscle aging start?
age 40
lab evaluation of myopathic disorders
serum CK electrolytes, thyroid serum Abs needle EMG nerve conduction study biopsy non-ischemic forearm test urine for myoglobin muscle imaging molecular/genetic studies
how might you get an excess of endogenous steroids
Cushings > bilateral adrenalectomy > excessive pituitary ACTH secretion > proximal myopathy (Nelson Syndrome)
which steroids are particularly likely to cause drug induced steroid myopathy
9-a-fluorinated corticosteroids
triamcinolone, betamethasone, dexamethasone
(long duration)
which steroids rarely cause myopathy
prednisone dose equivalent < 30 mg qd
complications of critical illness
CIM: critical illness myopathy
CIN: critical illness neuropathy
PNMB: prolonged neuromuscular blockade
mechanisms of steroid myopathy
not fully understood
likely due to impaired protein synthesis and muscle catabolism
which muscle fibers are more susceptible to steroid myopathy
type 2 fibers (fast, glycolytic)
cellular transcription changes caused by steroids that can induce myopathy
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
growth factor changes contributing to steroid myopathy
negative changes in IGF-1 and myostatin
muscle weakness pattern associated with Cushings
insidious onset
proximal muscle weakness and wasting without involvement of distal or cranial muscles
fat redistribution in Cushings
supraclavicular and temporal fossa
facial rounding
central obesity
buffalo hump
skin findings in Cushings
wide (>1 cm) purple striae
bruising
hirsutism
poor wound healing
pediatric findings in Cushings
decreased linear growth with continued weight gain
behavioral / psych effects of Cushings
decreased libido
lethargy
depression
other endocrine changes in Cushings
impaired glucose tolerance / diabetes
menstrual changes
muscle weakness seen in exogenous steroid myopathy
proximal, symmetric weakness
legs > arms
wasting and myalgias
systemic effects of exogenous steroids
weight gain HTN hyperlipidemia glucose intolerance diabetes osteopenia menstrual changes impotence
purpose of EMG
measure integrity of nerves, muscles, and their junction
what makes up a normal motor unit action potential
1 axon with its constituent muscle fibers
appearance of nerve injury on EMG
more fiber recruitment
extra amplification
polyphasic shape rather than triphasic
appearance of muscle injury on EMG
action potential amplitude decreased, but shape is the same
lab results seen in steroid myopathy
normal CK
normal or mild myopathy on EMG
muscle pathology of steroid myopathy
type 2 fiber atrophy
myosin loss
treatment of endogenous steroid myopathy
pituitary tumor removal in Cushings
ketoconazole
treatment of exogenous steroid myopathy
reduce dose of steroids
supportive care / physical therapy
mnemonic for generalized weakness in the ICU
MUCESS Medication (steroids, NMBA) Undiagnosed neuromuscular disorders (ALS, MG) Critical illness myopathy / neuropathy Electrolyte disorders Systemic illness Spinal cord damage
what is Guillain-Barre
ascending paralysis, often post infectious (GI or resp)
peripheral neuropathy and weakness that eventually progresses to resp failure
what is an example of a trigger of Guillain-Barre
vaccines (flu shots)
1/100,000
causes of muscle weakness after ICU admit
CIM CIP prolonged NM blockage acute necrotizing myopathy cachectic myopathy not GBS
medical conditions associated with CIM
sepsis renal/liver failure asthma organ transplant use of IV steroids and/or NMBAs
challenges associated with NM evaluation in the ICU
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
useful investigations in evaluating ICU weakness
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
how many pts get CIM?
up to 46% of patients evaluated for ICU weakness
clinical features of CIM
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
lab features of CIM
CK often mildly elevated within 9 days after exposure to steroids, but can remain normal or very low
aldolase may be elevated
which types of sensory nerves are tested by nerve conduction studies
a-alpha
a-beta
larger and faster conduction velocity
proprioception and touch sensing
which types of sensory nerves are ignored by nerve conduction studies
a-delta
C
smaller and slower conducting
pain and temperature sensing
