Neuromuscular Flashcards
What is myopathy?
Primary diseases of muscle; classically proximal symmetrical weakness but many exceptions
Genetic diagnoses relatively common regardless of age at presentation
What are genetic myopathies?
Muscular dystrophies (degenerative genetic myopathies) - Duchenne and myotonic dystrophy are 2 most common
Duchenne: X-linked, 1 in 3500 live male births, dystrophin deficiency, onset by age 5, usually inability to walk age 10, eventual respiratory failure - calf hypertrophy, cardiomyopathy. Steroids typically given in childhood
Becker muscular dystrophy: later onset milder form
Limb girdle muscular dystrophy: large group of conditions - Type 1 (dominant) and type 2 (recessive)
Myotonic dystrophy: dominant CTG repeat, commonest adult muscular dystrophy - distal muscle wasting / weakness, myotonia. Bilateral ptosis, frontal balding, cataracts, cardiac conduction defects, day time somnolence, gonadal atrophy, mental impairment. Cardiac rhythm monitoring essential
Facioscapulphumeral dystrophy: domintant, onset <20 years, usually involves face and upper limbs withs scapular winging, distal lower limb weakness (foot drop) also common, respiratory failure rare
What are metabolic myopathies?
Usually present in childhood, result from deficiencies of specific enzymes in carb/lipid/mitochondrial oxidative phosphorylation.Muscle weakness, may have myoglobinuria and rhabdomyolysis
McArdle’s disease: autosomal recessive, glycogen metabolism from myophosp
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What are inflammatory myopathies?
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Other acquired myopathies?
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Investigations for myopathy?
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What is myaesthenia gravis?
Symptoms and Tx?
Autoimmune - antibodies to skeletal muscle nicotinic AChRs - neuromuscular transmission failure: fatiguable weakness often fluctuates in severity
- Ptosis
- Complex opthalmoplegia
- Weakness of face / neck / bulbar muscles - dysphagia and dysarthria
Respiratory muscle can be affected - potentially fatal complication through TYPE 2 RESPIRATORY FAILURE
Thyoma present in proportion (usually benign)
Thymectomy increasingly proposed as Tx, sometimes even in young patients without demonstrable thyoma on imaging.
Tx: AChE inhibitors e.g. pyridostigmine and immunosuppression e.g. prednisolone. Short-term benefit from plasma exchange or IVIG. Initial paradoxical deterioration after steroid treatment
Diagnosis of MG?
AChR antibodies present in 80%, with generalised myasthenia but only 50% with purely ocular symptoms. A few ‘seronegative’ patients may have antibodies to muscle specific kinase (MuSK).
Repetitive nerve stimulation: decrementing response in compound muscle action potential amplitude
Single-fibre EMG more sensitive and may show increased jitter / blocking
IV Edrophonium (Tensilon) may reveal transient improvement - patiens should be pre-treated with atropine 300mcg to prevent serious cholinergic muscarinic effects e.g. bradycardia, hypotension
What is botulism?
Exposure to exotoxin from Clostridium botulinum (acts presynaptically, decreases ACh release) - GI upset, dilated non-reactive pupils, blurred vision, weakness beginning with extra-ocular and oropharyngeal muscles before becoming generalised
Tx with Botulism trivalent antitoxin
What is LEMS?
Lambert-Eaton Myasthenic Syndrome
Autoimmune, antibodies against pre-synaptic voltage-gated Ca channels - impaired neuromuscular transmission - often paraneoplastic.
Usually proximal limb weakness (legs > arms)
May have autonomic symptoms (dry mouth, impotence).
Deep tendon reflexes often absent but show post-tetanic potentiation (appear after sustained muscle contraction)
Incremental response on repetitive nerve stimulation is diagnostic
Tx: facilitate Ach release e.g. 3,4-diaminopyridine, pyridostigmine and immunosuppression
What is MND?
Also known as anterior horn cell disease, motor neuropathy
Common, life limited, ALS most common form
Clinical diagnosis: pure motor syndrome with combination of LMN signs (atrophy, fasiculation) and UMN signs: hyper-reflexia, in the same limb.
Bulbar involvement (dysarthria / dysphagia) common and carries poorer prognosis. Co-exists with frontotemporal dementia (FTD).
Death typically occurs through respiratory failure, can be temporarily alleviated with non-invasive ventilation.
Neurophysiological can support diagnosis though diffuse, chronic partial denervation in 3 or more limbs on EMG - 1:15 is genetic, most commonly C9orf72 gene.
What is spinal muscular atrophy (SMA)?
Inherited LMN form on MND
Typically childhood onset (type 1 <6 months, most severe) - type 2 can live into adulthood, type 3/4 don’t usually limit life expectancy
Adult onset may occur where progression is slower than ALS (type 4) significant breakthroughts in treatments have recently been made - Spiranza - not yet approved by NICe.
What is radiculopathy?
Conditions affecting nerve roots, extremely common usually from degenerative arthritic changes in cervical or lumbar spine - one or more roots
Polyradiculopathy can also be caused by meningeal disease - shooting / lancinating pain induced by limb movement, early loss of corresponding reflexes, then progressive sensory and motor deficits
Most radiculopathy managed with neuropathic pain medicine or local nerve root injection, Surgical intervention reserved for cauda equina syndrome, progressive neurological deficit or intractable pain.
What is plexopathy?
Disease affect brachial or LS plexus - regional motor sensory and reflex disturbance in one limb often very painful - pattern cannot be explained by single nerve root or peripheral nerve
Clinical diagnoses supported by EMG and/or NCS.
Contrast enhanced MRI of plexi can be helpful. D
iabetes is common cause, malignant infiltration should be considered e.g. Pancoast tumour
What is peripheral neuropathy
Diagnosis?
Very common group of diseases: often picked up incidentally, most present with slowly progressive, distal, symmetrical syndrome.
May include sensory/motor and sometimes autonomic. Sensory loss usually occurs first.
Without other coexisting pathology (e.g. cervical myelopathy, cerebral small vessel disease) - purely LMN signs and ‘glove and stocking’ sensory distribution.
Screen for most common treatable cases: FBC, U+E, LFT, TGT< HBA1c, B12, folate, serum and urinary immunofixation (Bence-Jones protein)
Neurophysiology (NCS/EMG) can identify whether neuropathy is axonal (degeneration of nerve axon itself) or demyelinating (typically inflammatory or immune in basis).
Pure sensory neuropathies (including sensory ganglionopathies) associated with underlying malignancy, some pure sensory neuropathies reflect the ‘small fibre’ pathology where neuropathic pain is common, reflexes are preserved and standard nerve conduction studies are preserved.
