Castleman’s Disease - Causes, Types

Castleman’s Disease Demystified: Classification, Pathology & Subtypes

Castleman’s disease is a rare disorder involving an overgrowth of cells in the lymph nodes. It is classified strictly as a rare blood disease, or more precisely, a rare lymphoproliferative disorder, which is closely linked to the blood and immune systems. This condition can cause symptoms like enlarged lymph nodes, fatigue, and fever, often mimicking blood-related disorders.

Why is Castleman’s Disease Considered a Blood Disease?

There are certain characteristics of Castleman's disease that confirm it is a blood disease. Here we will highlight those characteristics in detail:

• Lymph Nodes: The primary characteristic of Castleman disease is the enlargement of lymph nodes. They are a part of your lymphatic system and a crucial component of the immune and blood systems.
• Blood Abnormalities: Castleman’s disease can cause various blood abnormalities, including low red blood cell counts, high or low platelet counts, and elevated creatinine levels. Additionally, it exhibits signs of abnormal haemoglobin levels and albumin.
• Pathology: The microscopic examination of lymph nodes in Castleman’s disease highlights specific cellular changes and patterns. These lymph nodes exhibit morphological differences from normal lymph nodes.
   

What are the Different Types of Castleman’s Disease?

Castleman’s disease is mainly classified into two types: unicentric and multicentric. Unicentric Castleman’s disease involves a single, enlarged lymph node, often in the abdomen or chest region. On the other hand, multicentric Castleman’s disease affects multiple lymph node regions and can cause various complications.

Let us discuss in detail the subtypes of these two categories of Castleman’s disease:

• POEMS-associated Multicentric Castleman Disease (POEMS-MCD): POEMS-associated multicentric Castleman’s disease is a rare condition where patients have both POEMS syndrome and multicentric Castleman’s disease. POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal plasma disorder, and skin changes), along with MCD, involves nerve damage, organ enlargement and other endocrine problems.
• HHV-8-associated Multicentric Castleman Disease (HHV-8+MCD): It is a lymphoproliferative disorder linked to human herpesvirus-8 (HHV-8) infection. This shows signs of enlarged lymph nodes in multiple regions, potential organ dysfunction, and systemic inflammatory symptoms. HHV-8-associated MCD is most diagnosed in individuals who are immunocompromised, particularly those with HIV/AIDS. While it can occur in HIV-negative individuals, this is far less common.
• HHV-8-negative/Idiopathic Multicentric Castleman Disease (iMCD): HHV-8-negative, or idiopathic multicentric Castleman’s disease, is a rare disorder exhibiting characteristics including systemic inflammation and organ dysfunction due to cytokine storm, particularly due to elevated levels of IL-6. HHV-8-negative, or idiopathic multicentric Castleman's disease (iMCD), is a distinct subtype not associated with the human herpesvirus-8 infection. Its exact cause remains unknown.

What Causes Castleman’s Disease?

The exact cause of CD is still not properly known and is under research. However, various factors can develop CD in HIV or immunocompromised patients. These we will highlight in detail here:

• Cytokine Dysregulation: Abnormal levels of cytokines, signalling molecules that regulate immune responses, may contribute to abnormal cell growth and lead to Castleman’s disease symptoms, like inflammation. Increased production of interleukins in the bloodstream can result in chronic inflammation.
• Autoimmune Responses: Sometimes our body’s immune cells mistakenly attack our healthy, normal cells, leading to chronic inflammation and an immune response. Chronic inflammation can lead to the growth of abnormal cells and the formation of enlarged lymph nodes, leading to organ dysfunction.
• Gene Mutations: Experts believe that mutations in genes associated with interleukin-6 can lead to CD development, but the exact gene is not fully understood. Mutations in IL-6 and its receptors can cause overproduction of cytokines, leading to increased immune response and inflammation, which are common in Castleman’s disease.

The exact mechanism and genes responsible for the development of Castleman’s disease are still under investigation. Future research may reveal genes and pathways responsible for the development and progression of it.