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Plasma Cell Dyscrasias are a group of clonal disorders characterized by the abnormal proliferation of plasma cells producing monoclonal immunoglobulins (M-protein or paraprotein).

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These range from asymptomatic premalignant conditions like MGUS to malignant neoplasms like multiple myeloma, plasmacytoma, and AL amyloidosis. They are collectively referred to as Monoclonal gammopathies .

Pathophysiology

Plasma cells are terminally differentiated B cells that produce antibodies.
In plasma cell dyscrasias, a single clone produces monoclonal Ig (IgG, IgA, IgM, or light chains κ/λ).
The accumulation of plasma cells or their secreted proteins leads to organ dysfunction, especially bone, kidney, blood, and nervous systems.

Classification

Disorder	Key Features
MGUS	<3 g/dL M-protein, <10% plasma cells, no symptoms (premalignant)
Smoldering Multiple Myeloma (SMM)	≥3 g/dL M-protein or 10–59% plasma cells, no CRAB
Multiple Myeloma (MM)	≥10% plasma cells + CRAB or myeloma-defining event
Solitary Plasmacytoma	Localized bone or soft tissue plasma cell tumor
Primary AL Amyloidosis	Deposition of monoclonal light chains as amyloid fibrils in organs
POEMS Syndrome	Polyneuropathy + Organomegaly + Endocrinopathy + M-protein + Skin changes
Waldenström Macroglobulinemia	IgM-producing lymphoplasmacytic lymphoma with hyperviscosity
Heavy Chain Disease	Rare; production of incomplete heavy chains (α, γ, or μ chains)

Key differentials:

Feature	MGUS	SMM	MM	AL Amyloidosis	WM
M-protein	<3 g/dL	≥3 g/dL	Any	Light chains	IgM
BM Plasma Cells	<10%	10–59%	≥10%	Variable	Variable
CRAB symptoms	No	No	Yes	No	No (but hyperviscosity)
Organ Involvement	No	No	Yes	Yes (amyloid)	Yes (hyperviscosity, neuropathy)
Treatment	Observe	Observe	Systemic Tx	Systemic Tx	Plasmapheresis + Tx

🧪 Diagnostic Tools

Investigation	Relevance
Serum protein electrophoresis (SPEP)	Detects M-spike
Immunofixation	Identifies specific Ig type and light chain (e.g., IgG-κ)
Serum free light chain (FLC) assay	Detects light chain-only dyscrasias; κ:λ ratio
Urine electrophoresis (UPEP)	Detects Bence Jones protein (free light chains in urine)
Bone marrow biopsy	Quantifies clonal plasma cells; IHC for CD138, cytogenetics
Imaging (MRI/CT/PET-CT)	Detects bone lesions and extramedullary involvement

Clinical Manifestations

System	Manifestations
Skeletal	Lytic lesions, pathological fractures (MM, plasmacytoma)
Renal	Cast nephropathy, light chain deposition (MM, AL amyloidosis)
Hematologic	Anemia (bone marrow infiltration, renal dysfunction)
Neurologic	Peripheral neuropathy (POEMS, amyloidosis, hyperviscosity in WM)
Cardiac	Restrictive cardiomyopathy (amyloidosis)
Hyperviscosity	Blurred vision, headache, confusion (WM, IgM MM)