Muscle weakness Flashcards
What are the 2 types of descending tracts?
Pyramidal tracts
Extrapyramidal tracts
Where do the pyramidal tracts originate?
Cerebral cortex
What is the function of the pyramidal tracts?
Voluntary control of musculature of body and face
Where do the pyramidal tracts pass through?
Medulla oblongata
Name the 3 pyramidal tracts
Corticospinal tracts - lateral and anterior
Cortiobullar
Where do the extrapyramidal tracts originate from?
Brainstem
What is the function of the extrapyramidal tracts?
Involuntary and automatic control of all musculature such as muscle tone, balance, posture and locomotion
Name the 4 extrapyramidal tracts
Vestibulospinal and reticulospinal (these don’t decussate)
Rubrospinal and tectospinal (decessate)
Where does the corticospinal tract divide into the lateral and anterior?
Caudal part of medulla
What is the route of the lateral corticospinal tract?
Decussates at medulla and terminates in ventral horn at segmental levels
What is the route of the anterior corticospinal tract?
Remains ipsilateral decussates in cervical and upper thoracic segmental levels
Which cranial nerve is NOT part of the PNS?
CN II
Where does the spinal cord end?
L1
What information about muscle weakness is important to get in a history?
Onset - instant/gradual
Distribution - proximal/distal, symmetrical/asymmetrical, mono (local process)/poly (diffuse), cranial involvement (bulbar/ophthalmoplegia/facial)
Variability - fatigueability/relapse-remission
Additional features - sensory symptoms (paraesthesia/loss of sensation)
Contact - recent illness, PMH, FH, drugs, alcohol
What the the UMN signs?
Bulk - normal Tone - increased Strength - decreased No fasciculations Increased reflexes
What are the LMN signs?
Reduced (wasting) bulk Normal/decreased tone Decreased strength Fasciculations Decreased/absent reflexes
How is muscle power graded?
MRC grading
What does 0 mean on MRC grading?
Complete paralysis
What does 1 mean on MRC grading?
Flicker of contraction possible
What does 2 on MRC grading mean?
Movement possible if gravity eliminated - hold elbow up and see if can extend
What does 3 on MRC grading mean?
Movement against gravity but not resistance
What does 4 on MRC grading mean?
Movement possible against some resistance
What does 5 on MRC grading mean?
Power normal (not normally possible to overcome a normal adult’s power)
Name 2 causes of weakness
Neuropathies
Myopathies
Name 3 causes of neuropathies
Peripheral neuropathy
GBS
MG
MND
How are neuropathies classified?
Polyneuropathy (peripheral neuropathy) Mononeuropathy multiplex (mononeuritis multiplex) - at least 2 nerves Mononeuropathy - one single nerve
What is a peripheral neuropathy?
Disease affecting peripheral nerves
What might be the S&S of a peripheral neuropathy?
Chronic and slowly progressive
Starting in legs and longer nerves
Sensory/motor/both
What conditions cause predominantly motor loss in peripheral neuropathy?
GBS CIDP HSMN Diphtheria Porphyria
What condition cause predominantly sensory loss in peripheral neuropathy?
Deficiency states eg B12/folate Diabetes Alcohol/toxins/drugs Metabolic abnormalities eg uraemia Leprosy Amyloidosis
What is mononeuritis multiplex?
Painful, asymmetrical sensory and motor neuropathy
Subacute presentation
Immune/inflammation mediated
What causes mononeuritis multiplex?
Vasculitis eg churg strauss
Connective tissue disorder eg sarcoid
What is a mononeuropathy?
Individual nerve deficits in isolation
Upper limb nerves mostly affected at compression points
What is the most common mononeuropathy?
Median nerve entrapment at wrist
Carpel tunnel
What other nerves can get trapped in the upper limb and what does it look like?
Ulnar nerve at elbow (claw hand)
Radial nerve at axilla (wrist drop)
Which nerve entrapment in the leg is most common?
Common peroneal nerve (foot drop)
What investigations might you do in a neuropathy investigation?
Neuropathy screen (looks at screen) Vasculitis screen EMG/NCS CSF study Imaging/nerve biopsy
What happens in a neuropathy screen?
Bloods
- FBC, ESR
- U&E, glucose, TFT, CRP, serum electrophoresis
- B12/folate
- Anti-gliadin
- TPHA, HIV
What happens in a vasculitis screen?
FBC, ESR
U&E, Cr, CRP
ANA, ANCA, anti-dsDNA, RhF, complement, cryoglobulins
What is the treatment of neuropathy?
20% idiopathic with no treatment
Neuropathic analgesic - gabapentin, pregabalin, amitryptiline
Treat/remove underlying cause eg DM/B12 deficiency
Inflammatory neuropathy - prednisolone with steroid sparing agents
Vasculitis - prednisolone with immunosuppressant
What is GBS?
Autoimmune response causing demyelination
When might GBS occur?
Post infections - resp/GI eg campylobacter
How does GBS present?
Subacute (< 6 weeks) ascending paralysis/numbness/areflexia
Always ask about breathing and swallowing!!
What will NCS studies show in GBS?
Demyelination
What will LP show in GBS?
Raised CSF protein
How do you treat GBS?
IV Ig or plasmapheresis
Support
Monitor FVC
ITU review
How long can recovery from GBS take?
Weeks - years
What is myasthenia gravis?
Autoimmune disorder - antibodies against nicotinic acetylcholine receptors in the NMJ characterised by weakness and fatigueability of proximal limb, bulbar and ocular muscles
Potentially fatal but treatable condition
What is also common in MG?
Thymus dysfunction - hyperplasia/thymoma
What are the S&S of MG?
Generalised - fatigueable weakness - proximal limbs, neck and face (head drop, ptosis), extraocular (complex diplopia), bulbar (speech/swallow) particularly elderly Ocular At risk of other autoimmune diseases Facial expression - myasthenic snarl Ptosis, diplopia Tendon reflexes normal but fatigueable Symptoms worse towards end of day Respiratory difficulties May fluctuate in severity over time
What investigations should you do for MG?
Tensilon test (allow accumulation of Ach in NMJ) - give IV edrophonium (short-acting anti-cholinesterase) - muscle power increases within seconds
AchR antibodies (raised in 90%) and MuSK antibodies (anti-muscle specific tyrosine kinase)
EMG - looks at NMJ and NCS
CT thorax/MRI - hyperplasia/atrophy/tumour
How do you treat MG?
Acetylcholinesterase inhibitors - symptomatic treatment
Immunosuppressants - steroids (start slowly), azathioprine, methotrexate, mycophenolate
Thymectomy if onset < 50 and disease poorly controlled with anti-cholinesterases
What is a myasthenic crisis?
Severe weakness including respiratory muscles
High risk of death
Always ask about breathing and swallowing!!
What can cause a myasthenic crisis?
Infection
Natural disease cycle
Underdosing and overdosing of medication
How do you treat a myasthenic crisis?
Take change in myasthenic condition seriously
Urgent review by neurologists
Think about breathing and monitor FVC
Anaesthetist review
Plasmapheresis and IV Ig to identify and treat trigger of relapse
What is MND?
Degeneration of motor neurons in the motor cortex and anterior horns of spinal cord
Mainly clinical diagnosis
How does MND present?
UMN and LMN signs
No sensory, visual or bladder/bowel involvement
Asymmetrical weakness
Bulbar/limb onset
What investigations should you do for MND?
LP
NCS/EMG
MRI
What is the most common type of MND?
ALS
What is the survival rate of MND?
2-5 years
What are the most common muscle disorders?
Steroid myopathy
Statin myopathy
Metabolic and endocrine myopathies
Myotonic dystrophy
What are the uncommon muscle disorders?
Muscular dystrophies eg Duchenne, Becker, facioscapulohumeral musclar dystrophy
Inflammatory muscle disease - polymyositis/dermatomyositis
Mitochondrial disorders
What are the symptoms of muscle disorders?
Stairs, chairs, and hair Wasting common Facial weakness Neck weakness Contractures Scoliosis Eye movement disorders rare
What investigations should you do in muscle disorders?
CK EMG ESR/CRP Genetics DMD Biopsy
How do you treat muscle disorders?
Remove causal agent if is one
Supportive - physio, OT, back, renal, diet
Immunosuppress if inflammatory
How common is MG?
More common in women 2:1
Peak age of incidence 30 with another smaller peak of incidence in men over 60
Prevalence 4 in 100,000
What can cause MG?
Under 50 and in women - other autoimmune diseases eg pernicious anaemia, SLE, rheumatoid arthritis, thymic hyperplasia
Over 50 and in men - thymic atrophy or thymic tumour, rheumatoid arthritis, SLE
Transient MG - D-penicillamine treatment for Wilson’s
What is the pathology of MG?
Autoimmune disease mediated by antibodies to nicotinic acetylcholine receptor - anti-AChR antibodies, interfering with NMJ via depletion of working post-synaptic receptor sites
Achieved by immune complex deposition of anti-AChR IgG and complement at post-synaptic membranes causing interference with and destruction of receptors
Both B and T cells implicated
Blocks excitatory effect of Ach on the nicotinic receptors due to less receptors resulting in muscle weakness
How can you demonstrate fatigueability in MG?
Ask patient to count to 50 - as reach higher numbers, voice becomes less audible
Hold finger up high and ask patient to look at it without lifting head - after a few seconds will be unable to keep eyes raised
What might worsen MG symptoms?
Pregnancy, hypokalaemia, infection, emotion, exercise, drugs
What drugs might worsen MG symptoms?
Opiates, beta-blockers, gentamicin, tetracycline
What could be differentials for MG?
MS
Hyperthyroidism
Acute GBS
Lambert-Eaton myasthenic syndrome
What is Lambert-Eaton myasthenic syndrome?
Paraneoplastic condition most often seen with small cell lung cancer due to defective Ach release at NMJ
Causes defective Ach release at NMJ resulting in proximal limb weakness with some absent reflexes
Weakness tends to improve after exercise - unlike MG
What are the S/E of anti-cholinesterases?
Increased salivation, lacrimation, sweating
Vomiting
Miosis (excessive pupillary constriction)
Diarrhoea
