Myotonic Dystrophy (MD); Charcot-Marie-Tooth Flashcards
Myotonic dystrophy is a genetic disorder that usually presents in adulthood. Typical features are: [4]
Progressive muscle weakness
Prolonged muscle contractions
Cataracts
Cardiac arrhythmias
TOM TIP: The key feature of myotonic dystrophy to remember is the [1]
This may present in exams with a patient that is [1]
TOM TIP: The key feature of myotonic dystrophy to remember is the prolonged muscle contraction.
This may present in exams with a patient that is unable to let go after shaking someones hand, or unable to release their grip on a doorknob after opening a door. When doing an upper limb neurological examination always shake the patients hand and observe for difficulty releasing their grip.
Lecture
Describe the presentation of myotonic dystrophy [+]
Muscle wasting (face/neck + distal limb) and myotonia (cramping / delayed muscle relaxation following voluntary contraction or percussion)
- Myotonia can be generalized or focal, affecting the hands, tongue, facial muscles, or lower limbs.
Both DM1 and DM2 present with progressive muscular weakness; however, the distribution and severity may vary between subtypes:
- Distal Limb Weakness (DM1): In DM1 patients, distal limb weakness predominantly affects the flexor muscles of the fingers, wrists, and ankles. In advanced stages, proximal limb muscles may also be involved.
- Proximal Limb Weakness (DM2): Patients with DM2 typically exhibit proximal limb weakness affecting hip girdle muscles more than shoulder girdle muscles. The weakness pattern in DM2 often resembles that of limb-girdle muscular dystrophy.
Facial & Bulbar Weakness
* Facial muscle involvement in both subtypes may manifest as ptosis, facial diplegia, dysarthria, dysphagia or nasal regurgitation due to palatal insufficiency.
Multisystem disease – cataracts, diabetes, cardiac conduction defects, respiratory failure, endocrine dysfunction
- atrioventricular block or atrial fibrillation, dilated cardiomyopathy, and sudden cardiac death.
- Respiratory insufficiency due to diaphragmatic or intercostal muscle weakness is a significant concern in DM patients.
- DM patients may exhibit insulin resistance or type 2 diabetes mellitus, hypogonadism with testicular atrophy (DM1), primary ovarian failure (DM2)
How do you differentiate myotnic dystrophy from muscular dystrophy? [3]
While both MD and Myotonic dystrophy feature progressive muscle weakness, the pattern of muscular involvement varies.
- In Duchenne’s or Becker’s MD for example, proximal muscles are primarily affected while in Myotonic dystrophy distal muscles are initially involved.
Myotonias are a distinguishing factor as they do not occur in other forms of MD
Cardiac involvement is common to both conditions; however, conduction abnormalities and arrhythmias are more prevalent within the patient population with Myotonic dystrophy.
Lecture
How do you treat myotonic dystrophy [+]
Management
* Cataract surgery, diabetic meds,
* Pacemaker/Defibrillator,
* Non-invasive ventilation.
* Na+ blockers for myotonia (mexiletine/phenytoin)
PM:
* Mexiletine can be used for myotonia, but its use should be guided by a neurologist. Steroids are not recommended due to potential worsening of myotonia.
Describe the presentation of inclusion body myositis [3]
Pattern of weakness:
- Forearm, wrist, finger flexors, quadriceps, foot dorsiflexors.
- Can be asymmetrical (think distal asymmetrical weakness)
- The disease is progressive by nature, meaning those affected are likely to require a walking aid or wheelchair within 15 years to help conserve energy and stay mobile.
- Depression and a general feeling of unhappiness is very noticeable and can be an indication of the disease before any sign of muscle weakness.
How do you dx inclusion body myositis? [2]
Plasma Creatinine Kinase usually >10x normal
Histological diagnosis:
- accumulation of myelinoid bodies and amyloid deposition a.k.a. inclusion bodies - inclusion bodies contain beta amyloid, hyperphosphorylated tau protein, apolipoprotein E, presenillin 1, prion protein, α-synuclein similar to a number of CNS neurodegenerative diseases
Describe the electrolyte disturbance seen in rhabdomyolysis [3]
Describe why [3]
High serum P043- and high serum K+ (can be life threatening) and Low serum Ca2+
hypocalcaemia (myoglobin binds calcium)
elevated phosphate (released from myocytes)
hyperkalaemia (may develop before renal failure)
How do you tx rhabdo [3]
Management:
* Aggressive IV fluids + Treat underlying cause if possible.
* ECG/Cardiac monitoring.
* May need renal replacement therapy if severe
Myonecrosis in rhabdo is caused specifically by what? [2]
Myonecrosis – caused by
1) physical injury to muscle or
2) energy depletion through failure of the ATP-pumps and Ca2+ influx
Which medications most commonly cause a rhabdomyolysis picture? [1]
Statins
Describe the presentation of steroid-induced myopathies [3]
What dose & length of tx causes it? [2]
What would CK, EMG and Histology look like? [3]
What is the tx? [1]
Pattern of weakness:
- Proximal, usually symmetrical, muscle weakness – particularly quadriceps.
- Cushingoid appearance
- Spares cranial nerve muscles
Risk with >40mg/day for >6 weeks
Serum CK usually normal
EMG usually normal
Histologically: Selective atrophy of type II muscle fibres
Treatment:
- Dose reduction or withdrawal of corticosteroid
What is important to note about raised CK when dx rhabdo? [1]
elevations of CK that are ‘only’ 2-4 times that of normal are not supportive of a diagnosis and suggest another underlying pathophysiology
What does a normal, myopathic and neuropathic EMG look like? [3]
Neuropathic EMG – polyphasic, long duration, large amplitude
Myopathic EMG – polyphasic, short duration, small amplitude
Describe what is meant by Charcot Marie Tooth disease [1]
Charcot-Marie-Tooth disease is an inherited disease that affects the peripheral motor and sensory neurones.
- It is also known as hereditary motor and sensory neuropathy.
- There are various types, with different genetic mutations and pathophysiology, causing myelin or axon dysfunction.
- The majority of mutations are inherited in an autosomal dominant pattern.
Describe the presentation of Charcot-Marie-Tooth disease [+]
There may be a history of frequently sprained ankles
- Lower leg weakness, particularly loss of ankle dorsiflexion (with a high stepping gait due to foot drop)
Foot drop
High-arched feet (pes cavus)
Hammer toes
Distal muscle weakness
Distal muscle atrophy
Hyporeflexia
Stork leg deformity
Distal muscle wasting causing “inverted champagne bottle legs”
Peripheral sensory loss
Lecture:
- Symmetrical, length dependent (distal –> proximal gradient).
- Lower limbs before upper limbs.
- Deformity - claw toes, pes cavus, charcot joints, scoliosis
- Continuum from pure motor –> motor/sensory/pure sensory)
Other causes of peripheral neuropathy can be remembered with the ABCDE mnemonic [5]
A – Alcohol
B – B12 deficiency
C – Cancer (e.g., myeloma) and Chronic kidney disease
D – Diabetes and Drugs (e.g., isoniazid, amiodarone, leflunomide and cisplatin)
E – Every vasculitis
Describe the mx plan for CMT [5]
Neurologists and geneticists to make the diagnosis
Physiotherapists to maintain muscle strength and joint range of motion
Occupational therapists to assist with activities of living
Podiatrists to help with foot symptoms and suggest insoles and other orthoses to improve symptoms
Analgesia for neuropathic pain (e.g., amitriptyline)
Orthopaedic surgeons for severe joint deformities
CIDP – Chronic Inflammatory Demyelinating Polyradiculoneuropathy.
Describe the typical disease course and presentation [2]
Progressive weakness (proximal + distal) and sensory loss (distal) – Over >8 weeks – relapse - remitting
Describe the examination findings of CIDP – Chronic Inflammatory Demyelinating Polyradiculoneuropathy. [3]
Examination
- Symmetrical proximal >distal weakness
- Absent reflexes
- Symmetrical glove and stocking sensory loss
Tx for CIDP? [2]
Treatment: Steroids/Intravenous Immunoglobulin
(Immune mediated attack on myelin sheath
