PERIPHERAL NERVE AND SKELETAL MUSCLE PATHOLOGY
PERIPHERAL NERVE
Types of nerve injury processes:
▪ Segmental demyelination → diseases that effect Schwann cells
▪ Axonal degeneration → diseases that effect the neuron or axon
-Wallerian degeneration (breakdown of distal axon following traumatic transection)
-myelin breakdown → myelin ovoids
-denervation atrophy to muscles
INFLAMMATORY NEUROPATHY
eg. Guillain Barre Syndrome
Clin: distal limb weakness progressing proximally
-progressive paralysis before returning to normal
-25% mortality
Path:
-infm of peripheral nerve by mφ, lφ
-segmental demyelination
-if severe→axonal degeneration also
EM: myelin damage
How to handle a peripheral nerve biopsy.
MUSCULAR DYSTROPHY
MUSCULAR DYSTROPHIES
eg. DUCHENNE MUSCULAR DYSTROPHY
Clin: weakness in pelvic then shoulder girdles
-pseudohypertrophy of calf (fat in muscle)
-death secondary to resp. insufficiency
Genetics:
-dystrophin gene Xp21 region→mutated
-type I and II fibres → loss of x-striations
Path:
1. variation in fibre size
2. ↑no. of internalized nuclei
3. degeneration, necrosis, phagocytosis of muscle fibres
4. regeneration of muscle fibres
5. proliferation of endomysial connective tissue
6. cardiac fibrosis
NEUROMUSCULAR JUNCTION DISEASES
MYASTHENIA GRAVIS
Clin: weakness, ptosis, double vision
Pathophys:
-Ab to AChR + ↓ AchR
-assoc/ thymic HP, thymoma
-severe: type II atrophy
INFLAMMATORY MYOPATHIES
1. dermatomyositis
2. polymyositis
3. inclusion-body myositis
Clinical features:
Dermatomyositis
-heliotrope rash w/ periorbital edema
-prox. muscle weakness first, fine motor-distal weakness late
Polymyositis
-prox. muscle weakness first, fine motor-distal weakness late
Inclusion body myositis
-involvement of distal muscles first, asymmetric
Pathophys:
-autoreactive T and B cells
Pathology:
Dermatomyositis
Skeletal muscle-perifasicular atrophy and infm
- vascular infm
Skin-vacuolar interface dermatitis
Polymyositis
-inflm + normal, necrotic, regenerating fibres
-NO vasc. infm
EM: tubular filamentous inclusions
Inclusion body myositis
-vacuoles in myocytes
→ contain: basophilic granules + amyolid
EM: tubular filamentous inclusions