Clinical History:
This 64-year-old patient presents with progressive distal bilateral upper and lower extremity numbness and pain. They also reported lower extremity muscle weakness. Past medical history is significant for prior lumbar disc surgery, hypertension, MGUS, cardiac arrhythmia and prior COVID-19 pneumonia. Muscle and nerve biopsy were performed.
Question:
Based on Figures #1-3 what does this abnormal C5b-9 positive material represent?
A. Scar tissue
B. Necrotic muscle
C. Parasite
D. Amyloid
Figure 3:C5b-9 immunohistochemical stain 200x original magnification
Answer:
Based on Figures #1-3 what does this abnormal C5b-9 positive material represent?
D. Amyloid <– correct answer
Medium magnification image showing “salmon orange” colored staining of material on routine light microscopy and “apple green” birefringence with polarized light, consistent with the presence of amyloid deposition.
Medium magnification image showing strong immunostaining of amyloid for complement membrane attack complex (MAC / C5b-9).
Amyloid frequently shows positive immunohistochemical staining for complement membrane attack complex (C5b-9 or MAC). Activation of the complement cascade has been proposed as contributing to tissue dysfunction associated with amyloid deposition.
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