Other Myopathies + Denervation Flashcards
What is the etiology of Myasthenia Gravis?
acquired autoimmune Dz: develop Ab’s to Ach receptors at neuromuscular junction
(15% have thymoma)
What demographic is primarily affected by Myasthenia Gravis?
- younger women (20-30)
- older men (>50)
What is the primary symptom of Myasthenia Gravis?
abnormal muscular fatigability & weakness
What are the clinical manifestations of Myasthenia Gravis?
- can be very acute onset (days)
- m. weakness & fatigue
- Extraocular mm (ptosis, diplopia) fatigued w/ repeated H-pattern
- facial changes (mask-like, snarl)
How do antibodies in Myasthenia Gravis affect the neuromuscular junction?
- destruction of Ach receptors = less surface area
- ^gap between n. ending & m.
In a patient presenting with symptoms of Myasthenia Gravis, what do you need to rule out first?
stroke
How would a thymoma cause Myasthenia Gravis?
residual thymus/benign tumor results in ^T-cells
What are the possible treatments for Myasthenia Gravis?
- thymectomy
- corticosteroids
- methotrexate
- anticholinesterase drugs
- plasmapheresis (reduces anti-Ach receptor Ab’s)
What is another, better term for Myositis ossificans?
Heterotropic Bone Formation
What tissues does Myositis ossificans occur in?
muscle
What tissues does Heterotropic Bone Formation occur in?
- most often in muscle
- can occur in fascia, tendons, jt capsule, fat
What is Heterotropic Bone Formation?
metaplasia of soft tissue to bone following trauma (crushing; hip replacement)/contusion
Name the 3 stages of Heterotropic Bone Formation
- pseudosarcoma
- differentiation
- maturation
What is the time period for the pseudosarcoma stage of Heterotropic Bone Formation?
4-6 wks
What is the time period for the differentiation stage of Heterotropic Bone Formation?
2-3 mo
What is the time period for the maturation stage of Heterotropic Bone Formation?
variable
Where is the greatest damage during the pseudosarcoma stage of Heterotropic Bone Formation?
center of injury
Describe the pathogenesis of Heterotropic Bone Formation
- trauma –> hematoma
- ^^damage & cell death
- holes appear in sarcolemma –> fluid accumulates
- phagocytes make holes larger
- damaged tissue liquefied & replaced by sheets of non-specific cells
- after 15 days: ^^proliferation of mesenchymal tiss.
- minimal osteoid formation
What can aggravate the process of the pseudosarcoma stage of Heterotropic Bone Formation?
trauma, massage, stretching, surgery, ^activity, ultrasound
How does Heterotropic Bone Formation appear histologically during the pseudosarcoma stage?
looks like neoplasia
What can Heterotropic Bone Formation in the pseudosarcoma stage be mistaken for? Why?
Osteosarcoma
- rapid cell division in this stage
- hazy ossification in soft tissue looks like periosteal Rxn
How would you differentiate Heterotropic Bone Formation from an Osteosarcoma?
- HBF has a history of trauma
- Zonal phenomenon is opposite of osteosarc. which ossifies from inside out
Describe the pathogenesis of the differentiation stage of Heterotropic Bone Formation
- mesenchymal cells differentiate into fibroblasts, chondroblasts, osteoblasts (metaplasia)
- giant cells remove debris
- periphery mineralizes
- center remains as fluid-filled cyst (hematoma) or undifferentiated cells
What is zonal phenomenon?
During differentiation stage of Heterotropic Bone Formation, mature bone develops around periphery
(center remains filled with fluid or undifferentiated cells)
Describe the pathogenesis of the maturation stage of Heterotropic Bone Formation
develops periosteum separating from surrounding tissues
What are the potential outcomes of the maturation stage of Heterotropic Bone Formation?
- remain indefinitely
- shrink and disappear
- surgical removal (once matured)
What determines that Heterotropic Bone Formation is in the maturation stage?
periosteum = mature bone (trabecular + cortical)
What are the clinical manifestations of Heterotropic Bone Formation?
- muscle pain
- decreased ROM
- hard, palpable lump deep in muscle
- may be associated w/ neurologic dz
What are the radiographic characteristics of Heterotropic Bone Formation?
- hazy ossification in soft tissue early on
- cortical bone seen in mature stage
What is another name for Fibrodysplasia Ossificans Progressiva (FOP)?
Progressive Myositis Ossificans
What is the etiology of Fibrodysplasia Ossificans Progressiva?
- some cases inherited
- no Hx of trauma
What tissues are involved in Fibrodysplasia Ossificans Progressiva?
usually postural muscles (back & major jts)
What age group is affected by Fibrodysplasia Ossificans Progressiva?
symptoms begin in early childhood (as early as age 2 or by adolescence)
What is Fibrodysplasia Ossificans Progressiva?
progressive, sheet-like ossification of muscles causing severe functional disability
What is the prognosis of Fibrodysplasia Ossificans Progressiva?
generally fatal due to loss of pulmonary function
(not treated - any soft tissue work will worsen condition)
Denervation affects what fiber type(s)?
both type I and II
What are some potential etiologies of Denervation?
- diseases causing progressive muscle weakness and atrophy (ALS, spinal muscular atrophies)
- traumatic (n. root avulsion)
- compressive (carpal tunnel, peripheral neuropathies)
Traumatic and compressive denervation involves ____ neurons
LMNs (i.e., peripheral neuropathies)
What happens when skeletal muscle fibers become separated from LMNs (denervation)?
cells atrophy –> appear dark & angular histologically
During denervation, what happens if reinnervation does not occur?
atrophy progresses and muscle fibers are replaced by adipose tissue
Denervated fibers are initially ____, but as disease progresses they ____
- scattered irregularly
- cluster
What may happen if denervation proceeds slowly?
- reinnervation may keep pace
- sprouting n. root endings make contact & synapse w/ m. fiber at previous motor end plate
What happens as one motor neuron takes over a given field of fibers?
fiber type grouping
If denervation occurs after fiber type grouping, ____ will occur
grouped atrophy
