Neuromuscular pathology

Question 1

Answer 1

Inflammatory myopathy

Question 2

Answer 2

Inclusion body myopathy

Question 3

Describe the gross changes in ALS

Answer 3

Ventral spinal motor nerve roots and cranial motor nerves (e.g. hypoglossal nerve) are atrophic compared with sensory nerve roots, reflecting lower motor neuron degeneration.

Loss of axons in corticospinal tracts (i.e., upper motor neuron degeneration) leads to secondary demyelination in lateral corticospinal tracts of spinal cord, sometimes detectable as a chalky white discoloration on cross-sections of spinal cord.

Question 4

Muscle biopsy indicative of?

[This is an NADH stain which stains muscle type 1 (slow twitch) fibers darker than type 2 (fast twitch) fibers.]

Answer 4

Biopsy helps to determine a diagnosis of ALS.

• The characteristic findings are those of a neuropathic myopathy – fiber type grouping and grouped atrophy.
• In a normal muscle the type 1 and type 2 fibers are randomly mingled together.
• In any disease which produces a chronic, gradual loss of motor neurons, the remaining axons sprout and innervate the nearby deinnervated fibers producing patches of muscle fibers all innervated by the same motor neuron and therefore all of the same type (fiber type grouping).
• Eventually the axonal loss may reach the point where the remaining fibers can’t sprout any more and there will be a patch of muscle fibers which are all deinnervated and therefore atrophic producing grouped atrophy.

[Note that the presence of fiber type grouping indicates that there is a neuropathic myopathy and helps to rule out other diseases like polymyositis which can mimic early ALS.]

Question 5

Answer 5

Duchenne Muscular Dystrophy

Question 6

This is a ___________stain showing pathognomic ________, often seen in ___________

Answer 6

This is a trichrome stain showing pathognomoc “ragged red” fibers, often seen in mitochondrial myopathies