Multiple Myeloma and the Underlying Causes of Infections

Multiple myeloma, a type of blood cancer that affects plasma cells in the bone marrow, significantly compromises the body's immune defenses. As a result, patients with this condition are at a heightened risk of developing infections. Understanding the root causes behind this increased susceptibility is crucial for effective management and prevention strategies.

Weakened Immune Function Due to Abnormal Antibody Production

In multiple myeloma, malignant plasma cells produce excessive amounts of abnormal immunoglobulins (also known as monoclonal or M proteins). While these proteins are structurally defective and do not contribute to immune protection, their overproduction suppresses the synthesis of normal, functional antibodies such as IgG, IgA, and IgM.

This imbalance leads to hypogammaglobulinemia, a condition characterized by low levels of healthy immunoglobulins. With fewer protective antibodies available, the body becomes increasingly vulnerable to bacterial, viral, and fungal infections—particularly respiratory and urinary tract infections.

Reduced White Blood Cell Count and Impaired Immunity

Another major factor contributing to infection risk is bone marrow infiltration by cancerous plasma cells. As these abnormal cells proliferate, they crowd out healthy hematopoietic stem cells responsible for producing white blood cells, including neutrophils—the primary defenders against bacterial and fungal invaders.

Neutropenia: A Critical Vulnerability

The resulting condition, known as neutropenia, severely limits the body's ability to mount an effective immune response. Even minor infections can escalate quickly in neutropenic patients, sometimes leading to life-threatening sepsis if not promptly treated.

Impact of Chemotherapy on Blood Cell Production

Treatment for multiple myeloma often involves chemotherapy regimens such as melphalan, cyclophosphamide, or combination therapies like VCD (bortezomib, cyclophosphamide, dexamethasone). While effective at targeting cancer cells, these drugs are non-selective and also damage rapidly dividing healthy cells—including those in the bone marrow.

This suppression of bone marrow function leads to myelosuppression, which manifests as reduced counts of white blood cells, red blood cells (anemia), and platelets (thrombocytopenia). The compromised immune system during and after chemotherapy cycles creates a window of high infection risk.

Additional Risk Factors and Preventive Considerations

Beyond the biological mechanisms, other factors such as older age, prolonged hospital stays, use of central venous catheters, and corticosteroid therapy further increase infection susceptibility in myeloma patients.

To mitigate these risks, healthcare providers may recommend prophylactic antibiotics, antiviral medications, and vaccination protocols (e.g., pneumococcal, influenza, and COVID-19 vaccines) when appropriate. Close monitoring of blood counts and early intervention at signs of infection are essential components of comprehensive care.

In conclusion, the interplay between disease-related immune dysfunction and treatment-induced myelosuppression makes infection a persistent threat throughout the course of multiple myeloma. Awareness of these underlying causes empowers both clinicians and patients to take proactive steps toward reducing complications and improving quality of life.