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• The monoclonal IgM leads to:
  1. Hyperviscosity (IgM is a huge pentamer) → sluggish blood flow, blurred vision, headaches.
  2. Cryoglobulin formation → cold-induced vascular symptoms.
  3. Autoantibody activity → hemolysis (cold agglutinin disease).
  4. Infiltration of marrow and organs → anemia, hepatosplenomegaly, lymphadenopathy.

Parameter	Finding	Explanation
Serum protein electrophoresis (SPEP)	Monoclonal spike in the β or γ region	IgM paraprotein
Immunofixation	IgM κ (most common)	Confirms clonality
Bone marrow	Infiltration by lymphoplasmacytic cells	Mixed small lymphocytes + plasma cells
Viscosity	Elevated	IgM pentamers thicken serum
Anemia	Normocytic, normochromic	Marrow infiltration, hemodilution
Cryoglobulins	Often present	Monoclonal IgM precipitates in cold