58 - Diseases of the musculoskeletal system 2 Flashcards
Components of muscle fibre
Basal lamina Plasma membrane Mitochondria Sarcoplasmic reticulum Myofibrils Myonuclei
Functional systems of a myocyte
Ion fluxes Neuromuscular transmission Excitation-contraction coupling Oxidative phosporylation mRNA transport
Neurogenic atrophy
Two populations of small and large f Small angulated f Group atrophy Fibre grouping Target f Pyknotic nuclear clumps
Most common muscle biopsy site
quadriceps
Sarcolemma
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
DMD
Rarely biopsied as can test genes.
Chair-bound by 12 years old
Diseases of myonucleus
Limb girdle muscular dystrophy 1B or Emery-Dreifuss muscular dystrophy
Centronuclear myopathies (should be at the side) causing myotubular myopathy.
Emery-Dreifuss
XL
Weakness of proximal arm and distal leg muscle
Early contactures
Cardiomyopathy
Limb girdle muscular dystrophy
Heterogenous
Phenotypic overlap with spinal muscular atrophy and BMD
Histochemistry needed
Core disease
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)
Nemaline myopathy
AR Children Problem with sarcomere Resp. insufficiency High arched palate Kyphoscoliosis Loss of cell structure
Ion channel disorder
Cl- ad Na+ is associated with malignant hyperthermia also
Malignant hyperthermia
Abnormal susceptibility to certain anaesthetic agents.
Prolonged rise in intracellular Ca2+ ions
Rigid contractions and elevation in body temperatures
Complex molecular defects
Repeat expansion disease -> myotonic dystrophy, oculopharyngeal muscular dystrophy
Large telomeric deletion disease -> facioscapulohumeral dystrophy
Myotonic dystrophy
AD
Myotonia and progressie weakness of facial muscle
Onset - 20-30 yrs
Cardiac conduction defects
Myotonic dystrophy histology
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
Facioscapulohumeral dystrophy
AD
Affects myocardium
Associated with progressive deafness
Retinal vasculopathy
Developed disorders
XL myotubular myopathy
Congenital fibre-type disproportion
Disorders of catabolic mechanisms
Lysosomal disorders
Proteolytic disturbances
Neuromuscular transmission defects
Neurogenic muscle disease
Myasthenia gravis
Lambert-eaton myasthenic syndrome
Congenital myasthenic syndrome
Myasthenia gravis
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.
Eaton-Lambert myasthenic syndrome
Rare non-metastatic manifestation of malignancy, usually oat-cell carcinoma of the bronchus
Gives you atrophic fibres
Dermatomyositis
Inflammatory myopathy responsible for chronic debilitating disease
Associated with a scaly rash
Dermatomyositis histology
mononuclear infiltration of muscle with fibre necrosis and replacement fibrosis
Drug induced myopathies
Statin myopathy
Steroid induced
Most severe causes necrotising myopathy causing rhabomyolysis, myoglobinuria and renal failure - caused by heroin and renal failure
Motor neuron disease
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
