Myopathies

Question 1

Myopathy history

Answer 1

Negative symptoms
-weakness (functional issues)
-fatigue
-exercise intolerance
-atrophy

Positive symptoms
-hypertrophy
-cramps
-contractures
-stiffness
-myotonias (inability to relax)
-myalgias
-myoglobinuria

Time course
-acute, subacute, chronic
-fluctuating, episodic
-progressive, static
-childhood or adult onset

Systemic illness
-rheumatological: joint pain/swelling, rash, fever, weight loss
-genetic: cataracts, frontal balding, hormonal issues, cardiac issues
-mitochondrial: mental impairment, seizures, dysmorphism, scoliosis

Family history
-problems with walking, working, arm strength
-pattern of inheritance

Triggers
-drugs (prescribed and illicit)
-anaesthetics
-illness and fever
-exercise
-diet

Question 2

Myopathy investigations

Answer 2

Bloods
-CK (usually elevated)
-urine myoglobin
-AST/ALT/LDH (may be elevated)
-K and Ca (may cause weakness)
-TFTs (possible cause of myopathy)
-ESR/ENA/ANA
-Specific antibodies
-Gene testing

Nerve conduction studies
-motor and nerve studies
-repetitive stimulation
-needle EMG

Muscle MRI
-increased STIR/T2 signal with inflammation
-fatty replacement with chronicity

Muscle biopsy
-equivocal or negative gene studies

Question 3

Dermatomyositis features

Answer 3

Subacute onset

Proximal weakness

Accompanying or preceding rash
-photosensitive areas
-erythematous, oedematous, sometimes itchy
-heliotrope (purple/red upper eyelids)
-gottron sign (scaling, erythematous lesions over finger joints)
-mechanic hands (rough, cracked fingertips)

Extra muscular manifestations
-cardiac, pulmonary, GI, joints
-malignancy

Bloods
-Elevated CK and ANA
-Specific antibodies

Muscle histopath features

Muscle MRI features

Question 4

Antisynthetase syndrome

Answer 4

Some or all of
Inflammatory myopathy
Interstitial lung disease
Inflammatory arthritis
Raynauds
Mechanic hands

Specific antibodies

Muscle histopathology

Question 5

Immune mediated necrotising myopathy features

Answer 5

Acute or subacute

Severe proximal muscle weakness

Extra muscular involvement is rare

Very elevated CK

Specific antibodies

Minimal findings on muscle biopsy

Question 6

Inclusion body myositis features

Answer 6

Older men

Slow progression

Preferential quads, ankle dorsiflexors, finger flexor weakness

Neck, facial and bulbar weakness possible

Reduced patellar reflex early

Mild CK rise

Specific antibodies

Muscle MRI
-Anterior thigh muscle involvement

Muscle biopsy findings

Question 7

Overlap myopathy features

Answer 7

Systemic rheumatic disease

Mild muscle involvement

Mild CK rise

Specific antibodies

Question 8

Polymyositis

Answer 8

Rare

Diagnosis of exclusion

Subacute proximal weakness

Question 9

Myasthenia gravis overview

Answer 9

Epidemiology
-uncommon
-occurs at any age

Pathophys
-Autoantibodies to ACh receptor
-Blockade, internalisation and destruction of AChR

General features
-Ocular or generalised disease
-Fluctuating and fatiguing weakness improving with rest
-Progression over years

Diagnosis
-Antibodies
-Repetitive stimulation
-Single fibre EMG
-Ice pack test
-CT for thyoma

Treatment
-IVIg and PLEX for exacerbations
-Pyridostigmine
-Steroids
-Immunosuppression

Ocular features
-Pupillary function always normal
-Ptosis (fatigued upward gaze and ice pack sign)
-Diplopia with fatiguing (resolves with one eye closed)

Bulbar features
-fatiguing dysarthria and hypophonia
-dysphagia and jaw weakness
-expressionless, weak facial muscles, myasthenic sneer

Neck and limb features
-neck flex/extensor weakness
-proximal limb weakness (arms more than legs)

Respiratory features
-decreases FVC
-respiratory failure in myasthenic crisis

Question 10

Myopathy exam

Answer 10

Weakness
-generalised/focal
-proximal/distal/mixed
-symmetric/asymmetric
-ocular, bulbar, neck, respiratory involvement
-gait
-function

Additional
-hypertrophy, atrophy
-contractions, stiffness
-dysmorphism
-systemic illness