58 - Diseases of the musculoskeletal system 2

Question 1

Components of muscle fibre

Answer 1

Basal lamina
Plasma membrane
Mitochondria
Sarcoplasmic reticulum
Myofibrils
Myonuclei

Question 2

Functional systems of a myocyte

Answer 2

Ion fluxes
Neuromuscular transmission
Excitation-contraction coupling
Oxidative phosporylation
mRNA transport

Question 3

Neurogenic atrophy

Answer 3

Two populations of small and large f
Small angulated f
Group atrophy
Fibre grouping
Target f
Pyknotic nuclear clumps

Question 4

Most common muscle biopsy site

Answer 4

quadriceps

Question 5

Sarcolemma

Answer 5

Basal lamina - links muscle fibres to endomyseal connective tissue, survives muscle fibres necrosis and acts as a platform for satellite cell proliferation.

Plasma membrane forms a barrier between extra and intracellular space

Question 6

DMD

Answer 6

Rarely biopsied as can test genes.

Chair-bound by 12 years old

Question 7

Diseases of myonucleus

Answer 7

Limb girdle muscular dystrophy 1B or Emery-Dreifuss muscular dystrophy

Centronuclear myopathies (should be at the side) causing myotubular myopathy.

Question 8

Emery-Dreifuss

Answer 8

XL
Weakness of proximal arm and distal leg muscle
Early contactures
Cardiomyopathy

Question 9

Limb girdle muscular dystrophy

Answer 9

Heterogenous
Phenotypic overlap with spinal muscular atrophy and BMD
Histochemistry needed

Question 10

Core disease

Answer 10

not detected until child has started walking
AD
Central core is a well demarkated zone in the central of the muscle fibre devoid of NADH. Cores only occur in type I fibres.

Issue is malignant hyperthermia (can die from resp. paralysis)

Question 11

Nemaline myopathy

Answer 11

AR
Children
Problem with sarcomere
Resp. insufficiency 
High arched palate
Kyphoscoliosis
Loss of cell structure

Question 12

Ion channel disorder

Answer 12

Cl- ad Na+ is associated with malignant hyperthermia also

Question 13

Malignant hyperthermia

Answer 13

Abnormal susceptibility to certain anaesthetic agents.

Prolonged rise in intracellular Ca2+ ions
Rigid contractions and elevation in body temperatures

Question 14

Complex molecular defects

Answer 14

Repeat expansion disease -> myotonic dystrophy, oculopharyngeal muscular dystrophy

Large telomeric deletion disease -> facioscapulohumeral dystrophy

Question 15

Myotonic dystrophy

Answer 15

AD
Myotonia and progressie weakness of facial muscle
Onset - 20-30 yrs
Cardiac conduction defects

Question 16

Myotonic dystrophy histology

Answer 16

Selective atrophy of type I fibres
Type II hypertrophy
Paucity of type IIb fibres
Central nuclei are an early feature
Motheaten and targetoid fibres
Ring fibres common

Question 17

Facioscapulohumeral dystrophy

Answer 17

AD
Affects myocardium
Associated with progressive deafness
Retinal vasculopathy

Question 18

Developed disorders

Answer 18

XL myotubular myopathy

Congenital fibre-type disproportion

Question 19

Disorders of catabolic mechanisms

Answer 19

Lysosomal disorders

Proteolytic disturbances

Question 20

Neuromuscular transmission defects

Answer 20

Neurogenic muscle disease
Myasthenia gravis
Lambert-eaton myasthenic syndrome
Congenital myasthenic syndrome

Question 21

Myasthenia gravis

Answer 21

Autoimmune diseases with antibodies IgG against Ach receptor. Do not get any muscle contraction due to no Ach binding.
Muscle biopsy not an appropriate diagnostic test because it cannot be tested. Needs to be clinically diagnosed.

Question 22

Eaton-Lambert myasthenic syndrome

Answer 22

Rare non-metastatic manifestation of malignancy, usually oat-cell carcinoma of the bronchus
Gives you atrophic fibres

Question 23

Dermatomyositis

Answer 23

Inflammatory myopathy responsible for chronic debilitating disease
Associated with a scaly rash

Question 24

Dermatomyositis histology

Answer 24

mononuclear infiltration of muscle with fibre necrosis and replacement fibrosis

Question 25

Drug induced myopathies

Answer 25

Statin myopathy
Steroid induced

Most severe causes necrotising myopathy causing rhabomyolysis, myoglobinuria and renal failure - caused by heroin and renal failure

Question 26

Motor neuron disease

Answer 26

Progressive disease of middle to old age
Widespread degeneration of motor neurons
Involves ant. horn cells, brain stem nuclei and Betz cells.
Upper and lower motor neuron signs with wasting