Histiocytic Diseases - All One Needs to Know

Introduction:

Histiocytes are also known as “dendritic cells, " present as antigens and monocyte-macrophages, also known as tissue macrophage cells. The term histiocytes comes from the Greek word tissue cells. These cells may arise from the embryonic yolk sac, postnatal bone marrow, or fetal liver. Histiocytosis includes diverse proliferative disorders characterized by infiltration and accumulation of various monocytes, dendritic cells, and macrophages in the affected tissues. Over the years, histiocytic disorders have drastically changed to reflect a wide range of clinical manifestations and clinical severities of some disorders having the same pathological finding.

What Are Histiocytic Diseases?

A group of non-malignant disorders that occur due to an overproduction of the histiocytic white blood cells known as histiocytes are histiocytic disorders. Histiocytosis is a common disease occurring in myeloid cells, mostly mononuclear phagocytes that share histological features with dendritic cells and macrophages. This condition can affect people of all age groups. Normal histiocytes can tune up the body’s defense against multiple pathogens. However, many histiocytes can cause immune system issues and body tissue inflammation. These can affect a single part or can affect many parts of the body. Histiocytosis is not cancer but can behave and cause symptoms like cancer.

What Is the Classification of Histiocytic Disorders?

The histological features of pathological cells classify histiocytic disorders compared with their physiological counterparts. These disorders are broadly classified into hundreds of subtypes. But the most common three categories are:

• Class Ⅰ: Langerhans cell histiocytosis is the most common type of histiocytic disorder. They can be local and asymptomatic in isolated bone lesions and involve multiple organs. Other rare histiocytic disorders like Erdheim-chester disease and juvenile xanthogranuloma are considered variants of Langerhans cell histiocytosis.

• Class Ⅱ: Non-Langerhans cell histiocytosis is a syndrome of extreme immune activation. It is further divided into primary and secondary types.

• Class Ⅲ: Malignant histiocytic disorder.

Another classification depends on histiocytosis affecting children and adults. Histiocytosis is a rare group of blood disorders that can account for less than one percent of all cancers affecting lymph nodes and soft tissues. They often have similar symptoms that make it harder to get a correct diagnosis.

The most common types in children are:

• Rosai-Dorfman Disease - This condition mostly affects children but can also affect adults. It is a common type that can cause swelling in lymph nodes.

• Langerhans cell histiocytosis - The most common type of histiocytosis. It is common in children and is mild and asymptomatic.

• Juvenile xanthogranuloma (a rare skin disorder due to histiocytes).

The most common types in adults are:

• Adult xanthogranuloma (skin disorder due to histiocytes).

• Rosai-Dorfman disease (a benign condition that involves an overgrowth of white blood cells).

• Erdheim-Chester disease - Commonly affects adults and is a rare condition similar to LCH, and they range from mild to potentially life-threatening.

• Malignant histiocytic disorders.

• Langerhans cell histiocytosis.

The signs and symptoms of the condition depend on the histiocytic disorders, depending on the organs and systems involved, as well as the level of their involvement. In most cases, Langerhans cell histiocytosis can be localized and manifest as pain or asymptomatic, like isolated bone lesions. On the other hand, a few cases of LCH can also involve multiple organs and systems with clinically significant signs and symptoms. The exact cause of this histiocytosis is unknown. Some researchers state that they can occur due to genetic mutations. Mutation or changes in the cells can lead to abnormal behavior. Identifying the gene mutations can help to develop new treatments for histiocytosis. The treatment can help prevent harmful cell changes that allow histiocytosis to grow out of control.

Other symptoms include:

• Fever.

• Skin rashes.

• Headache.

• Shortness of breath.

• Swollen lymph nodes.

• Bone pain.

• Unexplained weight loss.

• Change in vision or bulging eyes.

• Frequent urination.

• Issues with balance and coordination.

How Is the Diagnosis Done?

The diagnosis is based on laboratory findings like:

• Check on hemoglobin.

• Differential cell count.

• Leukocyte count.

• Coagulation tests.

• LFT (live function tests).

• Urine osmolality test after overnight fasting.

• Imaging studies like chest, lateral, and posterior radiography and a skeletal examination. A special type of scan is called an FDG PET or CT (computer tomography) scan.

• Biopsy may be recommended in some cases. The tissue is accessed through biopsy, which also tests the genetic material in the blood, known as liquid biopsy.

How Is Histiocytic Disorder Managed?

• Treatment strategies for various disorders depend on the type of the disease, and the interpretation of optimal therapeutic strategies is often uncertain in most individuals. Cytotoxic therapies are mostly used to cure individuals with systemic ECD, LCH, and RDD. Treatment is decided after monitoring the symptoms one is experiencing. Surgery can be an option if the disorder is located in only one part of the body.

• Radiation therapy is sometimes used to destroy the histiocytosis cells, giving symptom relief.

• Chemotherapy sends chemicals through the bloodstream to destroy excess histiocytosis. Corticosteroids can reduce the inflammation associated with histiocytosis. These are mostly used with other treatments, such as combination therapy with chemotherapy. Targeted therapy corrects certain genetic mutations.

• Immunotherapy bolsters the immune system to identify and destroy harmful and abnormal histiocytes.

Conclusion:

Histiocytosis in many individuals achieves “durable remission,” which means they do not have any symptoms or signs of the illness. Surgery can cure a few forms of histiocytes. The provider may recommend scheduling the follow-up visits to analyze any disease that can occur. Histiocytosis is not curable, so a better plan is recommended to manage the condition. Histiocytosis is not preventable, but treatment can help in managing the symptoms. Avoiding smoking can reduce the risk of LCH (Langerhans cell histiocytosis) in the lungs. Choosing not to smoke can help individuals respond better to the treatment. The outcome of the condition of histiocytes can depend on various factors, for some individual histiocytes resolve on their own. Histiocyte disorders in adults and children require immense careful monitoring and intensive treatment. In severe cases, the condition can lead to organ damage.