NMJ Pathology

Question 1

Pt. complains of increased weakness as the day goes on with repeated use of muscles. Biopsy is not overly revealing. Some type 2 muscle atrophy is present and some focal points of inflammation are as well. With repeated stimulation, a characteristic decrease in CMAP amplitude occurs. Pt. complains of fatiguability in eyelids, extraocular muscles, swallowing muscles, expression, speech. Upon follow-up, respiration is even affected. Scans and biopsy reveal thymoma. What is the likely diagnosis? What is the pathophysiology? What is the Rx?

Answer 1

Myasthenia Gravis

• Antibodies attack postsynaptic ACh receptors causing loss of receptors
• Thymectomy (if thymoma), ACh-esterase inhibitors (neostigmine, pyridostigmine), immunosuppression, plasmapheresis

Question 2

Pt. complains of weakness and tingling sensation particularly in the legs, but some in the arms and face. She notes fatigue and xerostomia. Areflexia is present in some of the joints and she complains of difficulty voiding her bladder/colon. Biopsy reveals some type 2 fiber atrophy. Her movements improve w/ muscle use rather than worsens and study reveals characteristic CMAP amplitude increases with muscle use. Anti-Hu antibodies are present in the serum. What is the likely diagnosis? What is the pathophysiology behind the disease? What is a common cause? Treatments?

Answer 2

Lambert-Eaton
- Anti-Hu antibodies are attacking the brain and presynaptic NMJ
- Often paraneoplastic
Rx: treat cancer, steroids, plasmaphoresis, di-amino pyridine or pyridostigmine bromide (Mestinon)

Question 3

What are some common causes of avascular necrosis? Pathogenesis?

Answer 3

Trauma (scaphoid, femoral head commonly), corticosteroid therapy, dysbarism (the bends), sickle cell anemia

Insufficient O2 delivery, throboembolism, pressure on vessels, venous occlusion

Question 4

What type of bone is most commonly affected in avascular necrosis? Why? Where might new bone develop?

Answer 4

Medullary (marrow) most commonly affected as cortical bone has collateral supply

New bone may develop over dead trabeculae - aka creeping substitution

Question 5

What is a characteristic change seen on biopsy during avascular necrosis?

Answer 5

Preserved trabeculae w/ empty lacunae (no osteocytes) and dead marrow.

Question 6

Name the bone fracture appearance:

1. Complete, 2. Closed, 3. Compound, 4. Comminuted, 5. Displaced, 6. Stress, 7. Pathologic, 8. Spiral, 9. Greenstick

Answer 6

1. Extends through bone completely
2. Skin intact
3. Bone penetrates skin
4. Splintered
5. Ends are not aligned
6. Slowly develops with repeated loads
7. Secondary to other disease (cancer)
8. Torque force on axis of shaft - often a sign of abuse in children
9. Incomplete fracture leading to bent/angulated fracture

Question 7

Pt presents with subperiosteal abscess in the face and extension from the sinuses to the skin. Ischemic necrosis is likely cause of dead bone. Involucrum of new bone surrounds dead bone (sequestrum). Pt. also has fever, chills, and elevated WBC (sepsis). S/S of endocarditis (CP, SOB, palpitations) and amyloidosis (deposition of misfolded proteins in organs) are present as well. What is the likely diagnosis? What two cancers can develop secondary to this disease process?

Answer 7

Osteomyelitis

- Squamous cell carcinoma may arise in chronic draining sinus tract and sarcoma may arise in involved bone.

Question 8

What is the first stage (immediate) of bone fracture healing? What is occurring?

Answer 8

Hematoma - blood fills cavity of broken bone

Question 9

What is the second stage of bone fracture healing? What is occurring? What cells are involved? What is the end result?

Answer 9

Callous formation - macrophages resorb blood clot and fibroblasts begin forming soft callus made of collagen - fibrous granulation tissue w/ new blood vessels surrounded by macrophages form callus

Question 10

What is the third stage of bone fracture healing? What is occurring? Time frame? What cells are involved? What is the end result?

Answer 10

Bony callus - woven bone formation - soft callus invaded by blood vessel formation and osteoblasts - over weeks the fibrocartilage is replaced by trabeculae of woven bone

Question 11

What is the fourth stage of bone fracture healing? What is the end result?

Answer 11

Remodeling - Woven bone remodeled as compact and cancellous bone

Question 12

What are the complications of the following in regards to healing bone fractures?

• Misalignment
• Psueoarthrosis
• Nonunion
• Open Fx.
• Vascular injury
• Potential embolism?

Answer 12

Misalignment - poor bone alignment after healing
Pseudoarthrosis - due to cystic degeneration - false joint formation of callus
Nonunion - displaced fracture
Open Fx. - infection
Vascular injury - osteonecrosis
Fat emboli