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Neurology Secrets > Myopathies > Flashcards

Myopathies Flashcards

1
Q

What signs and symptoms are suggestive of myopathy?

A
  • Proximal myopathy
  • Symmetric
  • Preserved sensation and reflexes
  • Reduced, normal or increased muscle bulk
  • Muscle pain/cramps
  • Fatigue
  • Myoglobinuria
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2
Q

What are the categories of myopathies?

A
  • Inflammatory (polymyositis, dermatomyositis, inclusion body myositis, immune mediated necrotising myopathy)
  • Toxic myopathies (alcohol, zidovudine)
  • Endocrine myopathies (hypothyroidism, hypoadrenalism)
  • Infectious myopathies (trichinosis, AIDS)
  • Muscular dystrophies (Duchenne, myotonic, limb-girdle)
  • Congenital myopathies (central core, centronuclear myopathy)
  • Metabolic myopathies (phosphofructokinase deficiency)
  • Mitochondrial myopathies (Kearns-Sayre)
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3
Q

How to classify strength?

A

0 = No movement

1 = trace movment

2 = Able to move but not against gravity

3 = Able to move full range against gravity

4 = Able to move against some resistance

5 = Normal strength

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4
Q

What are the most common causes of muscle pain?

A
  • Most caused by nonmuscular condition; vascular insufficiency, joint disease, neuropathy
  • Most myopathies are painless
  • Painful myopathies: inflammatory myopathies, metabolic myopathies, mitochondrial myopathies, some muscular dystrophies
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5
Q

What investigations should be done for myopathies?

A
  1. Serum CK levels
  2. Electromyography (EMG)
  3. Muscle biopsy
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6
Q

Which myopathies are associated with raised CK?

A
  • Limb-girdle muscular dystrophy
  • Duchenne and Becker
  • Inflammatory myopathies
  • Rhabomyolysis
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7
Q

What is rhabdomyolysis

A
  • Severe acute muscle injury causing myalgia, muscle weakness, muscle swelling, myoglobinuria, raised CK >5x ULN
  • AKI as a result
  • Causes include crush injuries, ischaemia, alcohol/drugs/medications, metabolic disturbance, myositis, infections, toxins
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8
Q

What conditions other than myopathies have raised CK?

A
  • Exercise
  • Increased muscle bulk
  • Muscle trauma
  • Viral
  • AKI
  • Metabolic disturbance
  • Drug use
  • Licorice
  • Endocrine disorders
  • Malignant hyperthermia

CK levels generally <3 fold

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9
Q

How are inflammatory myopathies classified?

A

Dermatomyositis

Polymyositis

Immune-mediated necrotizing myopathy

Inclusion body myositis

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10
Q

What are the clinical features of polymyositis and dermatomyositis?

A

PM is adult disease, DM in both children and adults

Symmetric proximal muscle weakness over weeks to months

Pharyngeal or diagphragmatic weakness is common

Unique to DM are cutaneous manifestations

  • Heliotrope rash
  • Gottron’s papules
  • V sign
  • Shawl sign
  • Gottron’s sign

Rash worsens in sunlight, scaly red.

Systemic involvement: fever, wt loss, cardiac arrhythmias, conduction abnormalities, conjunctivitis/uveitis, ILD, GI, calcinosis. Most common is antisynthetase syndrome (anti Jo-1); ILD, non erosis arthritis, mechanic’s hands (hyperkeratotic lesions on palmar fingers)

Association with cancer: lung, breast, GI, ovarian

CK elevated

Anti Jo-1 (antisynthetase), Mi-2 (DM)

EMG shows low-amplitude, small myopathy units with evidence of fibrillation potentials and or positive sharp waves

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11
Q

What are the major pathologic changes on histology of patients with PM and DM?

A

Atrophic fibres, necrosis, phagocytosis

  1. DM - perivascular and perimysial inflammation
  2. PM - endomysial inflammation
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12
Q

How to treat DM and PM?

A
  1. Corticosteroids 1mg/kg/day
  2. Second line: IVIG, azathioprine, methotrexate, MMP, tacrolimus, rituximab, cyclosporine, cyclophosphamide
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13
Q

What is inclusion body myositis?

A
  • Most common cause of acquired chronic myopathy in 50yrs and older
  • Insidious painless weakness, atrophy involving quads, finger flexors, and foot dorsiflexors. Dysphagia is common.
  • CK levels normal or only mildly elevated
  • Biopsy - cytoplasmic rimmed vacoules and eosinophilic inclusion bodies.
  • Resistant to conventional immunotherapies.
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14
Q

What is immune-mediated necrotising myopathy?

A
  • Acute or subacute proximal weakness and myalgia with marked elevated CK and scattered necrotic muscle fibres.
  • Secondary to underlying CTD (scleroderma or MCTD) or cancer, but most likely triggered by statin use
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15
Q

What are the most common myotoxic agents?

A
  • Statins and fibrates - myalgias, rhabo, necrotizing myopathy
  • Steroids - type 2 fibre atrophy
  • Alcohol - rhabdo, prox myopathy - type 2 fibre
  • Chloroquine - vascular myopathy
  • Penicillamine - drug induced DM
  • Protease inhibitor - rhabdo
  • NRTIs - mitochondrial myopathy
  • Amiodarone
  • Colchicine, vincristine
  • Snake venom
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16
Q

What is statin myopathy?

A
  • Statin assoc myalgias and cramps occur in up to 20% of users, and dose dependent
  • Usually self limiting, and will resolve after discontinuation after a few weeks
  • However some patients have necrotising autoimmune myopathy that progresses even after statin is discontinued - anti-HMG-CoA reductase, need aggressive immunosuppression
17
Q

What neuromuscular conditions are associated with HIV?

A
  • Polymyositis
  • IBM
  • Mitochondrial myopathy due to ARV drugs
  • Diffuse infiltrative lymphocytosis syndrome
  • HIV wasting syndrome
18
Q

What is critical illness myopathy?

A

Severe flaccid paralysis that can affect all muscles including respiratory muscles.

19
Q

What is neuroleptic malignant syndrome?

A
  • Cardinal features hyperthermia, rigidity, autonomic instability, altered consciousness in setting of markedly elevated CK and recent exposure to triggering agent
  • Usually with antipsychotics
  • Anti-dopaminergics too: metoclopramide and promethazine
  • Tx: stop trigger, hydration, bromocriptine or dantrolene
20
Q

Explain Duchenne and Becker MD

A
  • Variations of the same disease - “alleilic”
  • Both caused by mutation in gene that produced dystrophin. X-linked recessive
  • Dystrophin needed to stabilise muscle cell membrane - otherwise sarcolemma weakness and allows CK to escape and Ca+2 to enter cell and cause cell death
  • Duchenne is the more severe form = no dystrophin. Symptoms begin in infancy or early childhood
  • Beckers - partial dystrophin. Symptoms begin 10-20yo.
  • Initially there is regeneration but overtime, muscles get fatty infiltration and fibrose = most evident in calf muscles. Waddling gait, contractures, scoliosis.
  • Dilated cardiomyopathy (functional MR), conduction abnormalities HOCM, pHTN, respiratory failure.
21
Q

What pharmacological treatment for DMD?

A
  • Steroids may slow progression
  • PT may improve QOL
22
Q

What is fascioscapulohumeral muscular dystrophy?

A
  • Progressive, often asymmetric, descending weakness involving face, shoulders, arms and distal legs.
  • Autosomal dominant. Chromosome 4
  • Signs
    • Myopathic facies - generalised wasting and weakness of facial muscles. No ptosis. No frontotemporal balding. Eye movements normal.
    • Wasting and weakness of upper limb girdle muscles and upper arms. Deltoids are well preserved, biceps are atrophied.
    • Superior margins of the scapulae are visible from the front above the clavicles and there is winging of the scapulae. Shoulder elevation = trapezius hump sign.
    • There is abdominal muscle weakness and lower abdominal muscles are weaker than the upper abdominal muscles.
    • Bilateral weakness of foot dorsiflexion with foot drop.

Other notes

  • Pain
  • Sensorineural hearing loss or visual loss - perform fundoscopy (retinal telangiectasia)
  • Shoulder weakness is presenting symptom - due to weak scapula fixation.
  • Winging of scapular due to weakness of trapezius.
  • Lower limb girdles muscles are not affected in 50% of patients
23
Q

Present Duchenne’s muscular dystrophy

A

This young patient is wheelchair bound. There is generalized wasting and weakness predominantly affecting the neck and proximal muscles of the upper and lower limb. The neck flexors are more affected than the neck extensors. The wrist extensors are more affected than wrist flexors. There are contractures of the lower limbs and there is pseudohypertrophy of the calf muscles. The deep tendon reflexes are reduced. There is kyphoscoliosis and there is an inability to generate a forceful cough. There is sparing of the facial musculature.

24
Q

Present Becker’s muscular dystrophy

A

This young patient is ambulant and has a waddling gait. There is wasting and weakness predominantly affecting the proximal muscles of the upper and lower limb. There is preserved power of the neck muscles. There is pseudohypertrophy of the calf muscles. The deep tendon reflexes are reduced. There is sparing of the facial musculature.

  • Waddling gait: wide based gait with trunk moving side to side, as pelvis drops on each side as foot leaves the ground. Hip extensor weakness results in forward tilt of the pelvis, resulting in hyperlordosis. Other causes of waddling gait = PM or osteomalacia.
25
Q

What are limb girdle dystrophies?

A

Genetically heterogenous disorders grouped together because they commonly present with slowly progressive, limb-girdle (or shoulder and pelvic muscle) weakness.

26
Q

Define myotonia

A

Impaird relaxation of muscle after forceful voluntary contractionand most commonly involves the hands and eyelids. Due to repetitive depolarisation of the muscle membrane.

27
Q

What are the inherited myotonic disorders?

A
  • Myotonic dystrophy type 1
  • Myotonic dystrophy type 2
  • Myotonia congenita
  • Paramyotonia congenita
  • Periodic paralysis
  • Chondrodystrophic myotonia
28
Q

What is the most common muscular dystrophy in adults?

How does it present?

A
  • Myotonic dystrophy type 1 is most common
  • Multisystem disorder with an autosomal dominant pattern of inheritance, but severity and degress of systemic involvement vary considerably
  • Most common presenting symptom is myotonia which is prominent in facial and distal arm muscles
  • Over time they develop distal muscle weakness and atrophy
  • Facial weakness, temporalis muscle atrophy
  • Frontal baldness, ptosis and neck muscle atrophy
  • Cardiac: conduction defects - AF, conduction block, PPM
  • Respiratory: weakness of respiratory muscles, CPAP
  • Gastrointestinal: abdominal pain, dysphagia, diarrhea, bowel incontinence
  • CNS: mentally retarded, apathy, personality disorder
  • Skeletal: atrophy, weakness, myotonia
  • Endocrine: testicular atrophy and insulin resistance
29
Q

Present myotonic dystrophy

A

This patient has myopathic facies, frontotemporal balding, ptosis, and cataracts. There is wasting of the facial muscles, temporalis, masseter, sternomastoids and the small muscles of the hands. There is difficulty in opening the eyes after firm closure. On examintion of the limbs there is distal wasting and weakness with impairment of fine movements of the hands and foot drop. The deep tendon reflexes are depressed. There is evidence of myotonia. There is high steppage gait.

Test neck flexion

Grip myotonia

Percussion myotonia

Foot drop = high steppage gait

Other:

  • Diabetes
  • Cardiomyopathy
  • Valvular heart disease: MVP
  • Arrhythmias: AF
  • Conduction defects: PPM
  • Hypogonadism: gynaecomastia, testicular atrophy
  • Goitre: nodular thyroid enlargement
  • Gastro: dysphagia, reflex, delayed emptying, hypomotility, malabsorption, bacterial overgrowth

Neurology Secrets (5 decks)

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