Hodgkin's Disease - Introduction

Subtypes of Hodgkin's Disease

Classical Hodgkin's Lymphoma. Based on the variations and numbers of Reed-Sternberg cells, as well as other features, four major subtypes of classical HD have been identified:

Nodular Sclerosis. Nodular sclerosis is the most common, representing almost 60% of HD cases. Younger patients are more likely to have this type. The nodes first affected are often those located in the center of the chest (the mediastinum).
Mixed Cellularity. Mixed cellularity is the next most common HD form, occurring in about 25% of patients, mostly in older patients, children, and those with immune disorders, such as AIDS. It usually indicates a more severe condition.
Lymphocyte Depleted. Lymphocyte-depleted HD occurs in about 4% of patients, nearly always in elderly people. It indicates extensive disease and a poor outlook. It can easily be confused with non-Hodgkin's lymphoma.
Lymphocyte-Rich Classical Hodgkin's Lymphoma. This form is similar to nodular lymphocyte predominant HD, but has more cell characteristics that conforms to classical HD.

Nodular Lymphocyte-Predominant Hodgkin's Disease. Nodular lymphocyte-predominant Hodgkin's disease (LPHD) occurs in about 5% of patients. The cells in LPHD known as lymphocytic and histolytic cells are proving to be distinctly different from classic Reed-Sternberg B cells. Patients with lymphocyte predominance are usually young men, who often have no symptoms. LPDH is very slow growing and may be associated with long survival. There is a 3% risk, however, that LPDH will transform to non-Hodgkin's lymphoma. In fact, lymphocyte-predominant HD may eventually be defined as a non-Hodgkin's lymphoma.

The Lymphatic System

Lymphomas represent tumors of the lymphatic system. This system is a network of organs, ducts, and nodes that interacts with the blood's circulatory system to transport a watery clear fluid called lymph throughout the body. The lymphatic system contains lymphocytes, which are important cells involved in defending the body against infections. This system also restores 60% of the fluid that leaks out from blood capillaries back into circulation. Its ducts provide transportation for fats, proteins, and other substances collected from the body's tissues.

Lymphocytes

The lymphatic system helps produce and transport lymphocytes, white blood cells that are a primary component of the immune system. Some lymphocytes produce antibodies that can target and attack specific foreignsubstances (antigens).

Lymphocytes develop in the bone marrow or thymus gland. They are categorized as either B cells (bone marrow-derived cells) or T cells (thymus gland-derived cells).
B cells complete their structural growth and definition (known as differentiation) and mature in the bone marrow.
T cells also start out in the bone marrow, but differentiate and mature in the thymus gland, located beneath the breastbone (sternum). This small gland is active mostly in the fetal stage through the first 10 years of life, after which it shrinks.
B-cell and T-cell lymphocytes leave these organs through the bloodstream, which eventually branches out into the tiny blood vessels called capillaries.
Some lymphocytes, along with fluid, proteins, and other substances, move out of the capillaries into the surrounding tissues. Some enter the lymphatic vessels.
Lymphatic vessels begin as tiny, blind-ended tubes. They lead to larger lymphatic ducts and branches, and drain into two ducts in the neck, where the fluid re-enters the bloodstream.
Along the way, the fluid passes through lymph nodes, which are oval structures composed of lymph vessels, connective tissue, and white blood cells. Here, the lymphocytes either are filtered out or are added to the contents of the node.

Lymph Nodes

In a lymph node, lymphocytes typically receive their initial exposure to foreign substances, such as bacteria. This exposure prompts the lymphocytes to perform their immune functions. The size of a lymph node varies generally from that of a pinhead to a bean. Most nodes are clustered throughout the body. Important node clusters are found in the neck, lower arm, armpit, and groin.

Other Structures in the Lymphatic System

The tonsils and adenoids are secondary lymphatic organs. They are composed of masses of lymph tissue that also play a role in the lymphatic system. The spleen is another important organ that processes lymphocytes from incoming blood.