June5 M1-NMJ and Muscle Flashcards
NMJ injury: charact of the typical things you look at for UMN vs LMN (weakness, atrophy, fasciculations, reflexes, tone + sensory involvement also)
- weakness has fatigue component (get even weaker with use)
- NO atrophy
- NO hyporeflexia
- NO fasciculations
- NO sensory involvement
muscle injury: charact of the typical things you look at for UMN vs LMN (weakness, atrophy, fasciculations, reflexes, tone + sensory involvement also)
- weakness is proximal
- ATROPHY
- NO fasciculations
- NO hyporeflexia
- NO sensory involvement
clinical case 1 of kid with proximal leg weakness (hip muscles), difficulty running, difficulty standing, falls and trips easily: what will you find on physical exam if muscle problem
- proximal weakness
- atrophy (thigh muscles). NMJ = no atrophy
- normal muscle tone
- normal reflexes (NO hyporeflexia)
- negative Babinski
- NO fasciculations
- NO sensory involvement (normal sensation)
clinical case 1: muscle atrophy indicates what
LMN involvement
+ NMJ problem less likely
clinical case 1: normal sensation indicates what
injury to root and nerves less likely (AHC still possible bc gives no sensory involvement)
clinical case 1: no fasciculations and normal reflexes indicate what
injury to AHC, root and nerves is less likely
clinical case 1: proximal weakness indicates what (points to what)
think of myopathy
clinical case 1 DMD (Duchenne muscular dystrophy) cause
- mutation in gene for dystrophin
- dystrophin is a protein that connects cytoskeleton (contractile) elements of the muscle cell to the cell membrane. (the cell membrane is connected to ECM via other proteins)
ddx for myopathies like case 1
- muscular dystrophies (inherited)
- inflammatory myopathies (dermatomyositis, polymyositis, inclusion-body myositis, etc.)
- toxic myopathies (medications like statins or steroids OR thyroid disease
- other hereditatory myopathies (metabolic like disorders of glycogen or fatty acid metabolsim, mitochondrial myopathies)
some common toxic myopathies
- steroid myopathy (proximal weakness)
- statin myopathy (from mild myopathy to muscle aches and pain to fulminant necrotizing inflammatory myopathy)
- hyper CK(creatine kinase)-emia
important questions in history and things to check when suspect a myopathy (muscle as cause of weakness and LMN problem)
- ask if difficulty standing up, going up stairs, getting into car, combing hair (proximal weakness)
- look for muscle atrophy
- think of medication induced myopathy
symptoms typical of an NMJ disorder
- fatiguable weakness. with a repetitive movement
- NO atrophy
- NO fasiculation
- NO hyporeflexia
- NO sensory involvement
clinical case 2: diplopia (see double) that resolves if cover one eye, symptoms worse in the evening, right eyelid droops and more at the end of the day: what makes you think of an NMJ problem?
- fatiguable weakness (gets worse at the end of the day)
- repetitive movement (muscles in eye lids)
different diseases of the NMJ
- Lambert-Eaton myasthenic syndrome (disease of Ca channels)
- botulism (Abs to proteins that dock vesicles so never released)
- myashtenia gravis (Abs to AchR)
- congenital (genetic) myasthenic syndromes
- anaesthesia (succinylcholine blocked the AchR)
myasthenia gravis (most well defined autoimmune disease) charact
- Abs to nAchR
- remove Ab = heals
- inject Ab = disease
- plausible mechanism = AchR-like Ags found in the thymus
- associated with thymomas and thymic hyperplasia
- presence of other Abs, which explains seronegative patients (without AchR Abs)
myasthenia gravis typical presentation
- starts with bulbar (head) symptoms: ptosis (drooling eyelid) and diplopia, fatigue
- can be very focal (dysphagia, head drop)
- no pain
- no sensory involvement (bc NMJ)
- possible respiratory muscle weakness
one quick trick to dx myasthenia gravis
ice pack test. cold temperature improves neuromuscular transmission. wait a bit and see if improves the diplopia and ptosis
botulism charact
-cause = 5 diff toxins produced by clostridium botulinum
-affect pre-synaptoc protein (whereas MG post synaptic) so muscarinic and nicotinic AchR synapses both affected so autonomic symptoms too
-
what could this be?: clinical case 3: woke up double vision, bilateral ptosis later in the day, next day nausea and vomiting, slurred speech, difficulty swallowing. exam = see these things + severe opthalmoplegia, unreactive pupils, bilateral facial weakness, severe weakness of shoulder and hip girdle muscles. normal distal strength, diminished reflexes, normal sensation
botulism
(think NMJ bc weakness, no sensory involvement and many muscle groups in diff places affected) botulism bc quick onset.
-note: hyporeflexia not characteristic of NMJ problem.
-note: proximal weakness typical of muscle prob
