Think about what sort of way muscle diseases could present?
- Babies may have poor feeding, failure to thrive & floppy
- SOB from resp muscles
- Poor swallowing or aspiration
- Cramp, pain, myoglobinuria
- Wasting or hypertrophy
- Reduced tone & reflexes
- Motor Weakness
What is myoglobinuria?
Myoglobin leaked from muscles that are breaking down due to certain muscle diseases.
Itll appear after exercise as black urine
List the classifications of muscle disorders?
(ion channel problems -> unrelaxable or weak muscles)
- Metabolic muscle diseases
- Inflammatory muscle diseases
- Congenital Myopathies
Name a drug that can cause iatrogenic muscle disease?
They can cause muscle degeneration leading to pain & weakness
What special blood test could you do for muscle disease?
Creatine Kinase (CK) Elevated in muscle damage
What investigations are common for muscular diseases?
- History & exam
- Creatine Kinase
- Genetic Tests (Most muscular dystrophies are genetic)
How does electromyography (EMG) work?
APs within a muscle measured (either surface or intramuscular) to assess its function.
It can be routine (tests a whole motor unit) or Single Fibre (Assesses just one motor fibre at a time)
List some muscular dystrophies?
- Duchenne’s MD & Becker’s MD
- Limb Girdle MD (Proximal limb weakness)
Describe a channelopathy?
Familial Hypokalemic Periodic Paralysis causes episodes of sudden muscle weakness lasting seconds -> days
Can also be Familial Hyperkalemic Periodic Paralysis
List some types of metabolic muscle disease?
Endocrinopathies such as thyroid or cushing’s disease can affect the muscles.
Carb or Lipid metabolism problems can affect the ability to produce ATP for muscle contraction.
Carb will be most pronounced on heavy exercise and Lipid on prolonged excercise)
What are the subtypes of Inflammatory Muscle Disorders?
Dermatomyositis (A paraneoplastic syndrome of muscle weakness and rash)
How would you investigate/treat Inflammatory Muscle Disorders?
Biopsy to inspect inflammatory cells, both diagnoses and differentiates between polymyositis and dermatomyositis.
Steroids and immunosuppresants
What is myasthenia gravis?
Fatigable weakness in skeletal muscles
Most often noticed in the eye muscle (cos they move so much) so your fine in the morning but by the afternoon you start getting ptosis and diplopia
Notably does not affect the reflexes, any sensory nerves or cause the muscles to waste
What causes myasthenia gravis?
An antibody blocks ACh receptors in the NMJ.
Its fatigable because early in the day you produce lots of ACh so it can compete with the antibody but by the end of the day its depleted and the antibody wins out so you get weaker until you rest again
What investigations can you do for Myasthenia Gravis?
- Antibody Tests
70% +ve & takes a while
- CT chest to exclude a thymoma
How does an EMG test for Myasthenia Gravis?
Repetetive stimulation should make the muscle fatigue, this will visible in a reduced amplitude on an EMG.
Also a single fibre EMG will show slight differences in how long each fibre takes to elicit an AP (called a “jitter”). This will actually show up before the patient becomes symptomatic, as they only get weakness when the fibres fail to elicit an AP at all
How do we treat Myasthenia Gravis?
- Acetlycholinesterase Inhibitors help with the symptoms
- Immunosuppression prevents antibody production (Prednisalone or Azathioprine)
- Thymectomy can prevent antibody production
- Immunoglobins or plasma exchange temporarily binds or filters out antibodies (for a severe attack)
Define Peripheral Neuropathy?
Damage to nerves outside the CNS. It can affect sensory axons, motor axons and ANS fibres
Can either be disease of a spinal root, single peripheral nerve or generalised peripheral neuropathy
What could cause a lesion to a single peripheral nerve?
- Compression or entrapment
- Vasculitis to the vessels supplying the nerve
What could cause generalised peripheral neuropathy?
- Diabetes (most common)
Toxic Drugs Infections e.g. HIV Inherited Paraneoplastic (e.g. prostate) Inflammatory demyelinating such as Guillain barre (acute) or Chronic Inflammatory Demyelinating Polyneuropathy
Define Guillain Barre Syndrome?
A type of peripheral neuropathy.
Its an autoimmune condition triggered by viral infection
(because the viral antigen is very similar to myelin)
Causes rapid onset muscle weakness/wasting, areflexia and sensory changes
What tests can be done for peripheral neuropathies?
- Blood Tests (particularly for inflammatory conditions)
- Genetic Analysis
- Nerve Conduction Studies e.g. EMG
- Lumbar Puncture for CSF analysis
- Nerve Biopsy
What is the main type of anterior horn cell disorder?
Motor Neuron Disease (Lou Gehrig’s Disease) (Amyotrophic Lateral Sclerosis - ALS)
Its a progressive loss of motor neurons (Upper & Lower)
How does ALS present?
It combines upper and lower motor neuron signs: # LMN - Fasciculations, Wasting, weakness # UMN - Increased Tone, Hyperreflexia # Theres no sensory involvement # Generalised to all muscles
Whats the prognosis for Motor Neuron Disease?
3 yrs median survival post-diagnosis
how do we diagnose ALS?
By the distinct combo of UMN/LMN signs plus a complete lack of sensory involvement.
How would you treat ALS?
- PEG Tube
- Non-invasive Ventilation
- Occupational Therapy
- Licensed for improving lifespan in ALS
- Very little evidence it works so must’nt oversell to patients