Lecture 7: Myesthenia Gravis, GBS, Myopathic disorders Flashcards
(23 cards)
Myesthenia Gravis: essentials of Dx
- fluctuating weakness of commonly used voluntary muscles, producing ax’s such as diplopia, ptosis, and difficulty swallowing
- activity increases weakness
- short acting anticholinesterases transiently improve the weakness
Myesthenia Gravis: general considerations
- occurs in all ages, sometimes in association with thymic tumor, thyrotoxicosis, RA or SLE
- most common in young women with HLA-DR3
- sx’s are due to ABs binding to Ach receptors so that Ach action is blocked
MG: signs/sx’s
- present with ptosis, diplopia ,difficulty chewing, swallowing, resp difficulties, limb weakness or combo of these
- weakness: localized or generalized
- most likely to be affected: ocular, masticatory, facial or pharyngeal muscles
MG: Phys exam
- sustained activity of muscles increases weakness, which improves after brief rest
- NO reflex changes
MG: Dx
- Tensilon test: administer tensilon ( which prevents breakdown of Ach), if ptosis gets better than is MG
- single fiber EMG
- Antibody measurement: AchR, MUSL
MG: Tx
Neostigmine and pyridostigmine = anti cholinesterase drugs
- immunosuppressant drugs
- thymectomy
- immunomodulation: PE or IVIg
Drugs that can worsen MG
- BB
- Corticosteroids
- Ca channel blockers
- aminogylcosides
- Magnesium
- curariform drugs
Guillain-Barre Syndrome (GBS): essentials of dx
- acute or subacute progressive polyradiculoneuropathy
- weakness is more severe than sensory disturbances
- acute dystautonomia may be life threatening
GBS: General considerations
- acute or subacute polyradiculoneuropathy sometimes follows infective illness, inoculations, or surgical procedures
- associated with preceding Campylobacteri jejuni enteritis
- probably has immunologic basis but mechanism is unclear
GBS: Epidemiology
- incidence: 1-4/100,000
- any age, peak in 4th decade; males > females
- 60-70% with antecedent infxn: C. Jejuni
- other causes: surgery, lymphos, lupus,
GBS: Signs/sx (AIDP)
AIDP= acute idiopathic demyelinating polyneuropathy
- LOSS OF DTRs
- paresthesias in feet then ascending
- weakness beginning distally then ascending
- can have other patterns: like onset in eye, face with descending pattern; or onset in hands and arms with descending and ascending pattern
- autonomic disturbances are common: tachycardia, cardiac irregularities, hypo/hyper-tension, facial flushing, sweating, pulm dysfxn, impaired sphincter control
GBS: Lab findings
- CSF: high protein
- nerve conduction studies: abnormal sensory condution (arm > leg); abnormal motor nerve conduction
GBS therapies
- IV Ig, PE
- supportive: PT, OT, swallow, dysautonomnia, skin, nutrition, vent. monitoring, support
GBS: prognosis
- 50% left with residual near signs: loss of reflexes, mild sensory loss, abnormal nerve conduction
- 10% have significant neuro deficit
- 5% mortality rate
GBS Variants: AMSAN/AMAN
AMSAN= acute motor and sensory axonal neuropathy
AMAN = acute motor axonal neuropathy
-caused by ABs to gangliosides on axon membrane
-similar to AIDP (clinical picture similar)
-pathophys: axon loss
GBS variant: Miller fisher syndrome
- this has ataxia, areflexia and opthalmoplegia
- also associated with anti-GQ1b ABs
Lambert-Eaton Syndrome : essentials of dx
- variable weakness, typically improving with activity
- a hx of malignant dz may be present
- dysautonomic sx’s may also be present
Lambert-Eaton: gen considerations
- may be associated with small cell carcinoma and occasionally with certain autoimmune dz.’s
- defective release of Ach caused by voltage gated Ca channel ABs–> leads to weakness, especially of PROXIMAL muscles of limbs
- unlike MG: power increases with sustained contraction
Lambert Eaton dx
-confirmed with electrophysiogically: muscle response to stimulation of its motor nerves increases if the nerve is stimulated repetitively at high rates
Lambert Eaton tx
- Plasma exchange and immunosuppressive therapy
- symptomatic therapy: K channel antagonists
Duschend Type MD
- X linked recessive
- onset = 1-5 y/o
- Distribution= pelvic, then shoulder girdle; later is reap muscles and limbs
- rapid progression, mortality within 15 yrs of onset
- intellectual retardation is common
- increase in serum creatinine kinase
Becker type MD
- X linked recessive
- onset = 5-25 yrs old
- pelvic then shoulder girdle weakness
- slow progression, may have normal life span
- dystrophin levels normal with increased serum CrK
Myotonic type MD
- autosomal dominant
- any age, usually 20-40 y/o
- face, neck and limb weakness
- slow progression
- other features: cataracts, frontal baldness, testicular atrophy, DM, cardiac abnormalities, intellectual changes
