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Neuro Exam 2 > Metabolic Myopathies > Flashcards

Metabolic Myopathies Flashcards

1
Q

metabolic myopathy defect classification

A

*carbohydrates (glycogen storage diseases, GSD)
*lipids (fatty acid transport, fatty acid oxidation, FAO)
*mitochondria (oxidative phosphorylation, OXPHOS)

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2
Q

metabolic myopathy classification - static vs dynamic clinical presentation

A

*static: fixed weakness, progressive; systemic involvement (heart, liver, brain, kidneys); more in newborns and infants
*dynamic: related to exercise (cramping, myalgia, intolerance, myoglobinuria); more in juveniles and adults

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3
Q

glycogen storage diseases (GSD or glycogenoses)

A

*most are autosomal recessive
*carbs are predominantly in liver and muscle tissues
*glucose is not being released and therefore cannot be used as an energy source (unable to create ATP)

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4
Q

GSD type I: Von Gierke disease

A

*glucose-6-phasophate deficiency
*CANNOT GET GLUCOSE OUT OF LIVER
*2nd most common form of GSD
*G6P only found in the liver, so no significant weakness
*pts present early in life with hepatomegaly, renal disease, growth restriction and typical facial features
*patients often have developmental delays

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5
Q

GSD type I: Von Gierke disease - labs

A

*hypoglycemia
*lactic acidosis
*hyperuricemia
*hyperlipidemia

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6
Q

GSD type I: Von Gierke disease - treatment

A

*diet, strict calories
*avoid hypoglycemia
*avoid fructose and galactose
*uncooked starch

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7
Q

GSD type II: Pompe disease - overview

A

*alpha-1,4-glucosidase deficiency (acid maltase deficiency)
*results in glycogen accumulation in the heart, liver, and muscles

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8
Q

GSD type II: Pompe disease - infantile presentation

A

*generalized weakness
*hypotonia (“floppy baby”)
*macroglossia
*cardiomyopathy
*weak/poor feeding
*respiratory failure

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9
Q

GSD type II: Pompe disease - juvenile presentation

A

*onset within first decade of life
*proximal muscles and calf hypertrophy
*Gower’s sign (Duchenne muscular dystrophy is most common cause of gower’s though)

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10
Q

GSD type II: Pompe disease - adult presentation

A

*proximal muscle weakness (similar to polymyositis)
*diaphragm involvement

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11
Q

GSD type II: Pompe disease - labs

A

*elevated CK
*a-glucosidase activity will be low (usually from dried blood spot test)
*high LFT
*high LDH

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12
Q

GSD type II: Pompe disease - treatment

A

*enzyme replacement therapy - alglucosidase alfa every 2 weeks
*one of the few that actually has an effective treatment

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13
Q

GSD type III: Cori-Forbes disease - overview

A

*debranching enzyme deficiency
*debranching enzyme has 2 functions:
1) glucanotransferase fxn
2) a-1,6-glucosidase fxn
*subtypes of disease based on enzyme deficiency location and specific activity (a-d)

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14
Q

GSD type III: Cori-Forbes disease - clinical features

A

*weakness noted in 3rd to 4th decade; 50% in DISTAL muscle groups in lower extremities
*ultimately, ventilatory muscles are involved
*can have associated cardiomyopathy

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15
Q

GSD type III: Cori-Forbes disease - labs

A

*reduced enzyme function of muscle, fibroblasts or lymphocytes
*elevated CK levels
*high liver function tests (LFTs)
*muscle biopsy: PAS positive vacuoles

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16
Q

GSD type III: Cori-Forbes disease - treatment

A

*low carb, high protein diet to help prevent fasting hypoglycemia
*uncooked cornstarch at bedtime

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17
Q

GSD type V: McArdle disease - gene/enzyme defect

A

*myophosphorylase deficiency
*associated with gene PYGM

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18
Q

GSD type V: McArdle disease - clinical presentation

A

*typically seen in childhood or young adults
*exercise intolerance with strenuous activity (weight lifting) or prolonged exercise (jogging, swimming)
*exertional muscle pain, cramping with “second wind” phenomenon

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19
Q

GSD type V: McArdle disease - labs

A

*excessively high CK levels (50k+), even when patients are not symptomatic
*myoglobinuria
*high LDH

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20
Q

GSD type V: McArdle disease - treatment

A

*control exercise (warm up)
*diet, sugar load prior to activity

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21
Q

GSD type VII: Tauri disease

A

*very similar to type V (McArdle): exercise-induced myalgia, cramping, jaundice
*typically is associated with fewer myoglobinuria and rhabdomyolysis
*due to lack of PFK in erythrocytes, can lead to hemolysis
*NO SECOND WIND phenomenon, but “out of wind” phenomenon (giving a sucrose load gives no benefit or makes symptoms worse)

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22
Q

disorders of lipid metabolism

A

*fatty acids are main source of energy for muscles at rest and following intense exercise or physical activity
*in normal lipid metabolism, fatty acid chains must move from cytoplasm to inner matrix of mitochondria
*long-chain fatty acids need help moving across the membranes
*once within the inner matrix, beta oxidation can occur, ultimately leading to ATP production

23
Q

carnitine transporter deficiency - etiology

A

*defects in OCTN2 (sodium dependent carnitine transporter protein)
*result: carnitine is not able to enter cells/cytoplasm and therefore cannot move fatty acids

24
Q

carnitine transporter deficiency - clinical features

A

*reduced feeding
*hepatosplenomegaly
*AMS (altered mental status)
*cardiomyopathy
*“hypoketotic hypoglycemia” when fasting

25
Q

carnitine transporter deficiency - labs

A

*low carnitine
*low ketones
*low glucose
*high NH4
*high CK

26
Q

carnitine transporter deficiency - treament

A

*L-carnitine
*avoid fasting
*low fat diet

27
Q

CPT1A deficiency - pathophysiology

A

*CPT1A = carnitine palmitoryltransferase 1
*pathology associated with type A isoform, which is found in the liver

28
Q

CPT1A deficiency - clinical features

A

*altered mental status (AMS)
*hepatomegaly
*no muscle symptoms
*often triggered by viral illness or fasting

29
Q

CPT1A deficiency - lab findings

A

*high carnitine
*low acylcarnitine
*low ketones
*low glucose
*mild NH4

30
Q

CPT1A deficiency - treatment

A

*avoid fasting
*low fat diet
*MCFA

31
Q

CACT deficiency - clinical presentation

A

*typically seen in neonates (up to 18 months)
*cardiac arrhythmias
*seizures
*severe muscle weakness
*hepatic dysfunction
*apneic episodes
*often triggered by infection, stress, fasting

32
Q

CACT deficiency - labs

A

*low carnitine
*high acylcarnitine
*low ketones
*low glucose
*high NH4
*high CK

33
Q

CACT deficiency - treatment

A

*low fat diet
*avoid fasting
*higher carbs
*controlled exercise

34
Q

CPT2 deficiency - overview

A

*most common cause of recurrent myoglobinuria/metabolic myopathy in adults

35
Q

CPT2 deficiency - clinical presentation

A

*usually in 2nd or 3rd decade of life
*intense muscle pain following prolonged fasting, infection, or intense prolonged exertion
*neonatal = death

36
Q

CPT2 deficiency - labs

A

*low carnitine
*high acylcarnitine
*low ketones
*low glucose
*high NH4 and CK

37
Q

CPT2 deficiency - treatment

A

*avoid fasting
*low fat diet
*high carbs
*controlled exercise

38
Q

disorders of fatty acid oxidation

A

*categorized based on the length of the fatty acid chain
*clinical presentations ranging from mild hypotonia in adults to sudden death in infants with hypoketonic hypoglycemia
*muscle biopsy often shows excess lipid within fibers
*treatment directed at high-carb diets

39
Q

examples of fatty acid oxidation disorders

A

*VLCAD (VLCA-CoA dehydrogenase deficiency)
*LCAD (LCA-CoA dehydrogenase deficiency)
*MCAD (MCA-CoA dehydrogenase deficiency)
*SCAD (SCA-CoA dehydrogenase deficeincy)

40
Q

clinical features of fatty acid oxidation disorders

A

*hypoglycemia
*hepatomegaly
*myopathy

41
Q

labs of fatty acid oxidation disorders

A

*NORMAL CK
other variable

42
Q

mitochondrial myopathies

A

*related to deletions or depletions of mtDNA and/or nDNA
*results in disruptions of oxidative phosphorylation, impaired ATP production
*only passed down maternally
*muscle biopsy can show ragged red fibers (RRF)

43
Q

Kearns-Sayre Syndrome and Progressive External Ophthalmoplegia (KSS/PEO) - genetics/defect

A

*single large deletion in mtDNA

44
Q

KSS/PEO - clinical features

A

*ophthalmoplegia
*proximal weakness
*respiratory muscle weakness
*sensorineural hearing loss
*endocrinopathy

45
Q

KSS/PEO - labs

A

*normal CK
*high lactate
*biopsy with RRF, COX negative fibers

46
Q

KSS/PEO - treatment

A

*creatine supplement
*surgery (ptosis)
*CV support

47
Q

myoclonic epilepsy and ragged red fibers (MERFF) - genetics/defect

A

*MTTK/ mtDNA point mutation

48
Q

MERFF - clinical features

A

*epilepsy
*proximal weakness
*sensorineural hearing loss
*optic atrophy

49
Q

MERFF - labs

A

*normal CK
*high lactate
*pyruvate
*abnormal EEG
*red ragged fibers on muscle biopsy

50
Q

MERFF - treatment

A

*creatine supplementation
*AED drugs (tx seizures)

51
Q

mitochondrial myopathy, lactic acidosis and stroke-like episodes (MELAS) - genetics/defect

A

*MTTL1, MtDNA point mutation

52
Q

MELAS - clinical features

A

*proximal weakness
*stroke-like episodes
*migraine headaches, nausea, vomiting, hemiparesis, hemianopsia, cortical blindness
*can have seizures/myoclonus
*rare eye findings

53
Q

MELAS - labs

A

*normal or high CK
*very high lactate in serum and/or CSF
*MRI findings (not localized to a vascular territory)

54
Q

MELAS - treatment

A

*L-arginine and citrulline
*AED drugs (tx seizures)

Neuro Exam 2 (24 decks)

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