Musculoskeletal Diseases Flashcards
What is the pathophysiology of myasthenia gravis?
Enough acetylcholine is present, but post-junctional nicotinic acetylcholine receptors are destroyed by IgG antibodies.
What SS present with myasthenia gravis?
First: diplopia and ptosis
bulbar weakness
dyspnea with exertion
proximal muscle weakness
What antibiotic can exacerbate myasthenia gravis? Why?
Aminoglycosides - they prevent normal Ach release presynaptically and block Ach receptors post-synaptically
What other situations exacerbate myasthenia gravis?
pregnancy (babies can be weak too for 2-4 weeks (lifespan of IgG))
infection
surgical stress
psychological stress
electrolyte abnormalities
What medication is used to treat myasthenia gravis? Why?
pyridostigmine - is an cholinesterase inhibitor (anitcholinesterase) -> increases parasympathetic neurotransmission by inhibiting Ach breakdown
What is the Tensilon test? How is it conducted?
Used to determine if acute weakness is due to pyridostigmine overdose (cholinergic crisis) or exacerbation of myasthenic SS (myasthenic crisis)
Administer 1-2 mg Edrophonium
If muscle weakness worsens, is cholinergic crisis (more Ach at NMJ made weakness worse). Treat with anticholinergic.
If muscle weakness improves, was myasthenic crisis. Increasing Ach at the NMJ improved the muscle strength.
What surgical treatment is indicated for myasthenia gravis?
Thymectomy - reduces circulating Anti-AchR IgG in most patients
Via median sternotomy or transcervical approach
What medications are used for immunosuppression in a patient with myasthenia gravis?
corticosteroids
cyclosporine
azathioprine
mycophenolate
Which patients with myasthenia gravis should be counseled on potential need for postop ventilation?
disease duration > 6 years
daily pyridostigmine > 750 mg/day
vital capacity < 2.9L
COPD
surgical approach: median sternotomy > transcervical thymectomy
In what disease is muscle weakness worse in the morning and improves through the day?
Eaton-Lambert syndrome aka myasthenic syndrome aka Lambert-Eaton Myasthenic syndrome
What is the pathophysiology surrounding Eaton-Lambert syndrome?
IgG mediated destruction of presynaptic voltage-gated Ca channels (normal receptors postsynaptically)
What treatment is indicated for Guillain Barre?
plasmapheresis
IV IgG
steroids and interferon not useful! contrary to multiple sclerosis
What is another name for Guillain Barre?
acute idiopathic polyneuritis
What is the treatment for both hypo- and hyper-kalemic periodic paralysis? Why?
Azetazolamide
creates non-gap acidosis = protection for hypokalemic
facilitates renal K excretion = protection for hyperkalemic
How should you manage body temperature in hypo/hyperkalemic periodic paralysis?
normothermia
avoid hypothermia at all costs!! even on CPB
Discuss the pathophysiology of malignant hyperthermia:
T-tubule is depolarized -> Ca enters myocyte via dihydropyrodine receptor
defective ryanodine receptor (RYR1) is active -> instructs sarcoplasmic reticulum to release way too much Ca
cell attempts to return Ca to sarcoplasmic reticulum via SERCA2 pump
+ more Ca to engage cardiac myocytes
substantial amount of ATP is used
increased O2 consumption
increased CO2 production
damaged sarcolemma allows potassium and myoglobin to escape (these are renal toxic) and enter systemic circulation
What are consequences of increased intracellular Ca in the myocyte?
rigidity from sustained contraction
accelerate metabolic rate and rapid depletion of ATP
increased O2 consumption
increased CO2 and heat production
mixed respiratory and lactic acidosis
sarcolemma breaks down
potassium and myoglobin leak into systemic circulation
What conditions ARE associated with MH?
King-Denborough syndrome
Central core disease
Multiminicore disease
Which conditions are NOT associated with MH?
Duchenne Muscular Dystrophy
Becker Muscular Dystrophy
Myotonic dystrophy
Myotonia congenita
Neuroleptic malignant syndrome
Osteogenesis imperfect
What are the risk factors for MH?
Geographical - Wisconsin, Nebraska, West Virginia, and Michigan
Male sex
Youth
What are early signs of MH?
increased EtCO2 disproportionate to minute ventilation
tachycardia
tachypnea
masseter rigidity
warm soda lime
irregular heart rhythm
What are intermediate signs of MH?
cyanosis
patient warm to touch
irregular heart rhythm
What are late signs of MH?
muscle rigidity
overt hyperthermia
cola-colored urine
coagulopathy
irregular heart rhythm
What are differential diagnoses to MH?
neuroleptic malignant syndrome
serotonergic syndrome
thyroid storm
pheochromocytoma
sepsis
cocaine intoxication
heatstroke
metastatic carcinoid
What is the sequence of MH treatment?
- DC triggering agent
- Call for help
3a. Hyperventilate with 100% FiO2 and min 10L FGF
3b. Apply charcoal filters, then new breathing circuit and reservoir bag - Administer Ryanodex or dantrolene
- Cool the patient (til 38C)
- Correct lactic acidosis
- Treat hyperkalemia
- Protect against dysrhythmias
- Maintain UOP > 2 mL/kg/hr
- DIC - late sign, impending demise
Discuss dantrolene or Ryanodex administration:
2.5 mg/kg IV every 5-10 min
stop dantrolene when signs of hyper metabolism subside
continue in ICU at 1 mg/kg q 6 hr or 0.1-0.3 mg/kg/hr for 48-72 H
(can reoccur up to 36 hours)
use largest vein possible (venous irritation is common)
if require >20 mg/kg, reconsider MH diagnosis
MH meds:
hyperthermia: cold IVF, cold fluid lavage stomach and bladder, ice packs
lactic acidosis: NaHCO3 1-2mEq/kg IV titrated to ABG and base deficity
hyperkalemia: CaCl 5-10 mg/kg IV, insulin 0.15 unit/kg + glucose 1mL/kg, hyperventilation
dysrhythmias: procainamide 15 mg/kg IV, lidocaine 2 mg/kg IV, NO CCB
maintain UOP: IV hydration, mannitol 0.25 g/kg IV, furosemide 1 mg/kg IV
hyperventilation: facilitates CO2 elimination, increases O2 deliver, drives K into cells
Discuss the pathophysiology of muscular dystrophy:
absence of dystrophin (anchor of actin and myosin to cell membrane) destabilizes sarcolemma during muscle contraction and increases membrane permeability
sarcolemma breakdown allows creatine kinase and myglobin to enter systemic circulation
calcium freely enters the cell, activating proteases which destroy contractile elements and lead to inflammation, fibrosis, and cell death
Discuss the respiratory considerations of muscular dystrophy:
kyphoscoliosis - restrictive -> decreased pulmonary reserve -> increased secretions and risk of pneumonia
respiratory muscle weakness
Discuss the cardiac considerations of muscular dystrophy:
degeneration of cardiac muscle -> reduced contractility, papillary muscle dysfunction, mitral regurgitation, cardiomyopathy, CHF
cardiomyopathy signs: resting tachycardia, JVD, S3/S4 gallop, point of maximal impulse displacement
Discuss the EKG changes of muscular dystrophy:
impaired cardiac conduction -> sinus tach and short PRI
scarring of posterobasal aspect (back/bottom) of LV -> increased R wave amplitude in Lead I, deep Q waves in limb leads
Discuss the GI considerations of muscular dystrophy:
impaired airway reflexes and GI hypomotility -> increased aspiration risk
Which type of scoliosis is most common? What other types exist?
idiopathic (80%)
congenital
myopathic (muscular dystrophy and amyotonia congenita)
neuropathic (cerebral palsy, syringomyelia, Friedreich’s ataxia)
traumatic
What Cobb Angle is indicative of surgery?
40-50 degrees
What early respiratory changes accompany scoliosis?
Restrictive: decreased FEV1 and FVC (FEV1/FVC ratio normal)
Decreased VC, TLC, FRC, RV
Decreased chest wall compliance
What CV changes accompany scoliosis?
RV hypertrophy (due to increased pulmonary vascular resistance)
mitral valve prolapse (most common)
mitral regurgitation
coarctation of the aorta
What vital capacity indicates postop ventilation in a patient with scoliosis?
<40%
How does rheumatoid arthritis affect the airway?
temporomandibular joint
cricoarytenoid joints
cervical spine
What is the most common airway complication of RA?
AO subluxation and separation of the atlanto-odontoid articulation
What late respiratory changes accompany scoliosis?
V/Q mismatch
hypoxemia
hypercarbia (impending respiratory failure)
reduced response to hypercapnia
pulmonary hypertension
cor pulmonale
cardiorespiratory failure
What stressors and drug exposures are known to exacerbate systemic lupus erythema?
PISSED CHIMP
Pregnancy
Infection
Stress
Surgery
Enalapril
D-penicillamine
Captopril
Hydralazine
Isoniazid
Methyldopa
Procainamide
Which immunosuppressant increases the duration of succinylcholine?
Cyclophosphamide - inhibits plasma cholinesterase
What disorder has an increased bleeding tendency due to poor vessel integrity?
Ehlers-Danlos syndrome
What type of anesthesia is not safe in multiple sclerosis?
spinal (epidural okay)
What three things increase the risk of contractures in myotonic dystrophy?
sux - use nondepolarizer
NMB reversal with anticholinesterases - use sugammadex
hypothermia - shivering -> sustained contractions
What is CREST syndrome and which condition is it associated with?
scleroderma
Calcinosis
Raynaud’s
Esophageal hypomotility
Sclerodactyly
Telangiectasia
