defining feautres of NMJ syndromes
fatiguable muscle weakness
myasthenia gravis
antibodies to the post-synaptic nicotinic Ach receptor; this leads to complement-mediated attack and internalization of the receptors
most common clinical manifestations of MG
ocular involvement is most common, manifesting as ptosis and diplopia; bulbar muscle weakness; limb weakness is usually proximal and symm; DTRs preserved
myasthenic crisis
presentation of MG with respiratory muscle weakness; medical emergency; must obtain FVC and neg inspir force
cholinergic crisis
state of increased cholinergic drive due to overmed with choliesterase inhib; also characterized by the presence of increased bronchial secretions, salivation, diarrhea, n/v, and diaphoresis
diagnostic eval of MG
edrophonium chloride (Tensilon) is an anti-Ach administered IV and the patient is observed for improvement in muscle strength; antibodies against nAChR
antibodies directed against MuSK and Lpr4
may be present in some patients with MG
repetitive nerve stim
reveals a decremental response that is seen in MG
Single fiber electromyography
most sens clinical test of NM transmission; characteristic finding in MG is increased jitter (a measure of the variability of NM transmission)
treatment for MG
anti-acetylcholinesterase drugs like pyridostigmine; immune modulating therapy; plasmapharesis and IVIg, steroids; thymectomy
Lambert-Eaton myasthenic syndrome
usually assoc with small cell lung cancer; caused by antibodies to presynaptic voltage-gated calcium channels
clinical presentation of lambert-eatin myasthenic syndrome
fatigable proximal weakness; DTRs are reduced or absent;
what is major difference bt Lambert-Eaton and MG?
bulbar and ocular sx are rare in LE, but autonomic complaints are common (dry eyes, dry mouth, impotence);
characteristic finding in LE
muscle faciliation (with brieg intense exercise, muscle strength increases and reflexes may appear transiently)
diagnosis of LE
antibodies to anti-voltage-gated calcium channel; decremental response on slow repeititive nerve stim and an incremental response on fast repetitive nerve stimulation helps to establish the diagnosis
treatment for LE
initial therapy is directed at underlying malignancy which is usually present in LE; when no malignancy is found, use steroids, azathioprine, IVIg, and plasmapheresis
most effective treatment in LE
3,4-diaminopyridine (and may be more effective if used together with pyridostigmine)
muscle biopsy in DMD and BMD
decreased staining for dystrophin
treatment for DMD and BMD
glucocorticoids slows the decline in musle strength
most frequent genetic cause of limb girdle muscular dystrophies
mutations in calpain-3 or sarcoglycans
limb girdle muscular dystrophies
shoulder and hip girdle weakness with relative sparing of extraocular, pharyngeal, and facial muscles
myotonic dystrophy genetics
either unstable CTG expansion in the DMPK gene or a CCTG expansion in the ZNF9 gene; disordered RNA processing
clinical features of myotonic dystrophy
weakness and stiffness of distal muscles; proximal develops later; systemic findings like cataracts, ptosis, arrhythmias, dysphagia (esoph myotonia); neurobehavioral features
important treatment in myotonic dystrophy
cardiac pacing; drugs like mexilitine, phenytoin, and carbamazepine may reduce the myotonia
most common adult onset muscular dystrophy
myotonic dystophy
fascioscapulohumeral muscular dystrophy
aut dom; weakness in face, scapula, and humerus; asymmetric weakness; over time, it descends;heart is usually spared
diagnosis of facioscapulohumeral muscular dystrophy
genetic testing. Deletion of D4Z4 repeat on 4q35
Emery-Dreifuss muscular dystrophy
mutations in emerin getne on the X chrom; or mutations in the lamin A and lamin C genes on chrom 1
clinical characteristics of Emery-Dreifuss muscular dystrophy
early onset of joint contractures, slowly progressive humeroperoneal pattern of weakness and atrophy, and cardiomyopathy that manifests as conduction abnormalities
what does humeroperoneal mean?
affects the bicepts, triceps, peroneal, and tibial muscles
female carriers of emery-dreifuss muscular dystrophy
do not develop weakness or atrophy but are at risk for cardiac complications
diagnosis of emery-dreifuss
CK levels mildly to moderatley elevated, EMG is myopathic, and muscle biopsy shows nonspec dystrophic changes
staining in emery-dreifuss
reduced or absent immunostaining fro emerin;
treatment for emery-dreif
none really; range of motion and stretching exercises may help with contractures; pacemakers for patients w severe conduciton abnormalities
Periodic Paralyses
characterized by episodic muscle weakness
cause of periodic paralyses
mutations in skeletal muscle membrane ion channel; attacks usually associated with a change in serum potassium
examples of mitochondrial myopathies
myoclonic epilepsy with ragged red fibers (MERRF); mitochondiral myopathy encephalopathy, lactoacidosis, and stroke (MELAS); progressive external ophthalmoplegia (PEO); and the Kearns-Sayre syndrome
findings in mitochondrial myopathies
co-occurrence of a myopathy and a peripheral neuropathy; serum lactate and pyruvate are often increased
examples of immune-mediated inflamm myopathies
polymyositis, dermatomyositis, and inclusion body myositis
clinical findings in polymyositis and dermatomyositis
proximal (usually symm) muscle weakness
clinical presentation of inclusion body myositis
weakness is asymm; may affect both prox and distal muscles; early selective involvement of forearm and finger flexors, as well as of knee extensors (quads)
how is IBM often diagnosed
when patients thought to have PM fail to respond to steroids
purplish discoloration of the eyelides (heliotrope) and papular erythematous scaly lesions over the knuckles (Gottron patches)
characteristc of dermatomyositis
other features of DM
cardiac manifestations, interstitial lund disease
anti-Jo-1 antibodies
seen in patients with dermatomyositis that have interstitial lung disease
which of the inflamm myopathies is most commonly assoc with other autoimmune diseases
polymyositis
pathogenesis of dermatomyositis
antibodies and complement against intramuscular blood vessels; inflamm is due to muscle ischemia
pathogenesis of polymyositis
mediated by CD8 T cells
pathogenesis of inclusion body myositis
both inflamm and neurodegenerative disorder
diagnosis of inflamm myopathies
CK elevated; EMG shows myopathic changes
diagnosis of PM on biopsy
endomysial inflamm with invasion of nonnecrotic muscle fibers with CD8+ T cells
diagnosis of IBM on muscle biopsy
endomysial inflamm and basophilic rimmed vacuoles
treatment for PD, DM, and IBM
steroids for PM and DM but they don’t help in IBM; IVIg helpful in DM
thyrotoxic myopathy
proximal muscle weakness and atropy with normal or brisk relexes; bulbar and resp muscle involvement is uncommon;
pathogenesis of thyrotoxic myopathy
unknown, but may reflect enhanced muscle catabolism
how to treat thyrotoxic myopathy
treat underlying thyrotoxic state with beta blockers to improve muscle strength
hypothyroid myopathy
prox muscle weakness, fatigue, myalgias, and cramps; reflexes may demonstrate delayed relaxation; CK typically elevated; may be associated distal polyneropathy
steroid myopathy
increased glucocorticoids from endogenous production or exogenous adminsitration; risk reduced with alternate-day regimens;
symptoms in steroid myopathy
weakness is predominantly proximal, with sparing of ocular, bulbar, and facial muscles
steroid myopathy muscle biopsy demonstrates what
type II fiber atrophy, but this finding is nonspec
drug or toxin induced myopathy
proximal myopathy and increased serum CK level
CK level in the metabolic myopathies
typically normal except elevated in hypothyroidism
neuroleptic malignant syndrome
syndrome characterized by fever, depressed level of arousal, muscle rigidity, and autonomic dysfunction
what usually causes neuroleptic malignant syndrome?
treatment with antipsychotics (haloperidol etc) but may also occur with L-dopa withdrawal in patients with parkinsons and in assoc with TCAs
etiology of neuroleptic malignant syndrome
central dopaminergic blockade
treatment of neuroleptic malignant syndrome
discontinue offending drup, aggressive fluid resus and other supportive measures, usually in an ICU; IV benzos may be helpful
what is the drug that causes necrotizing myopathy?
HMG-CoA reductase inhib, cyclosporine, propofol, alcohol
steroid myopathy caused by what
fluorinated glucocorticoids
drug that causes mitochondiral myopathy
ZDV
drug that causes inflamm myopathy
cimetidine, procainamide, L-dopa, phenytoin, lamotrigine, D-penicillamine
drug that causes critical illness myopathy
corticosteroids plus neuromuscular blocking agents in patients with sepsis
nerve stimulation in LE
decremental response following slow repetitive nerve stimulation and an incremental response following
nerve stimulation in MG
decremental response following slow RNS
MG with elevated anti-MuSK antibodies
typically less than 40 yo African American; present w early respiratory dysfunction and often do not respond to cholinesterase inhib like pyridostigmine
why would you get a chest CT in a patient wth MG?
thymoma and thymic hyperplasia assoc with anti-AchR antibody MG