Histiocytosis Explained

In medicine, histiocytosis is an excessive number of histiocytes^[1] (tissue macrophages), and the term is also often used to refer to a group of rare diseases which share this sign as a characteristic. Occasionally and confusingly, the term histiocytosis is sometimes used to refer to individual diseases.

According to the Histiocytosis Association, 1 in 200,000 children in the United States are born with histiocytosis each year.^[2] HAA also states that most of the people diagnosed with histiocytosis are children under the age of 10, although the disease can afflict adults. The disease usually occurs from birth to age 15.^[3]

Histiocytosis (and malignant histiocytosis) are both important in veterinary as well as human pathology.

Diagnosis

Histiocytosis is a rare disease, thus its diagnosis may be challenging. A variety of tests may be used, including:^[4]

• Imaging
  • CT scans of various organs such as lung, heart and kidneys.
  • MRI of the brain, pituitary gland, heart, among other organs.
  • Skeletal survey is useful in children
  • Ultrasound of liver and spleen
• Blood tests: measure cell counts and inflammation
• Breathing tests
• Tissue biopsy and molecular testing to detect mutations

Classification

There are competing systems for classifying histiocytoses. According to the 1999 classification proposed by the World Health Organization, they can be divided into three categories.^[5] However, the classifications in ICD10 and MeSH are slightly different, as shown below:

Name	WHO			-	Langerhans cell histiocytosis (LCH)	I		Langerhans-cell histiocytosis	-	Juvenile xanthogranuloma (JXG)	II		non-Langerhans-cell histiocytosis	-	Hemophagocytic lymphohistiocytosis (HLH)	II		non-Langerhans-cell histiocytosis	-		II		non-Langerhans-cell histiocytosis	-		II	–	non-Langerhans-cell histiocytosis	-		III		malignant histiocytic disorders	-		III		malignant histiocytic disorders	-		II		malignant histiocytic disorders

Alternatively, histiocytoses may be divided into the following groups:^[6]

• X-type histiocytoses
• Non-X histiocytoses

Lymphohistiocytosis is a similar immune system disease characterized by the inappropriate activation of natural killer cells, CD8+ cytotoxic T-cells, and macrophages, involving principally the liver, spleen and central nervous system and associated with severe lymphoid atrophy.^{[7] [8]}

Treatments

Various treatments exist for histiocytosis. The one selected depends on the location of the disease and the patient history. The modalities used may include:^[9]

• Chemotherapy
  • Cladribine (also known as 2CDA or Leustatin)
  • Etoposide
  • Methotrexate
  • 6-mercaptopurine
  • Vinblastine
• Surgery
• Radiation therapy

Society

Patients and families can gain support and educational materials from the Histiocytosis Association.

The Histiocyte Society, a nonprofit organization, is a group of more than 200 physicians and scientists from around the world committed to improving the lives of patients with histiocytic disorders by conducting clinical and laboratory research into the causes and treatment of this disease. The Society has instituted several clinical trials and treatment plans.^{[10] [11]}

The North American Consortium for Histiocytosis (NACHO) is a group of institutions that collaborate on scientific and clinical research for histiocytic diseases. Established in 2014 by 12 institutions, it was funded through a consortium grant from the St. Baldrick's Foundation.^[12]

Notes and References

1. Web site: Histiocytosis . https://web.archive.org/web/20161009025354/http://www.emedicinehealth.com/script/main/srchcont_dict.asp?src=histiocytosis . 2016-10-09 . eMedicine Dictionary .
2. http://www.histio.org/page.aspx?pid=378 Disease information
3. Web site: Histiocytosis – Signs and Symptoms . 2007-05-07 . https://web.archive.org/web/20070928015409/http://www.ucsfhealth.org/childrens/medical_services/cancer/histio/conditions/histio/signs.html . 2007-09-28 . dead . UCSF Children's Hospital . The Regents of the University of California .
4. Web site: Histiocytosis Diagnosis . 15 February 2022 . Memorial Sloan Kettering Cancer Center .
5. Harris NL, Jaffe ES, Diebold J, Flandrin G, Muller-Hermelink HK, Vardiman J, Lister TA, Bloomfield CD . 6 . The World Health Organization classification of neoplastic diseases of the hematopoietic and lymphoid tissues. Report of the Clinical Advisory Committee meeting, Airlie House, Virginia, November, 1997 . Annals of Oncology . 10 . 12 . 1419–1432 . December 1999 . 10643532 . 10.1023/A:1008375931236 . free .
6. Book: James WD, Berger TG, Elston DM, Odom RB . Andrews' Diseases of the Skin: clinical Dermatology . Saunders Elsevier . 2006 . 10th . 978-0-7216-2921-6 .
7. Book: Konkol S, Rai M . Lymphohistiocytosis . May 2022 . StatPearls [Internet] . Treasure Island (FL) . StatPearls Publishing . 32491708 . https://www.ncbi.nlm.nih.gov/books/NBK557776/ . 15 February 2022 .
8. Goldberg J, Nezelof C . Lymphohistiocytosis: a multi-factorial syndrome of macrophagic activation clinico-pathological study of 38 cases . Hematological Oncology . 4 . 4 . 275–289 . 1986 . 3557322 . 10.1002/hon.2900040405 . 30623642 .
9. Web site: Histiocytosis Treatment . 15 February 2022 . Memorial Sloan Kettering Cancer Center .
10. Web site: Tebbi CK . 16 September 2020. Kanwar VS . What is the Histiocyte Society classification of histiocytosis syndromes?. 4 December 2020. Medscape.
11. Book: Chang KL, Snyder DS . https://books.google.com/books?id=cR_kOJoN7sYC&pg=PA382. Rare Hematological Malignancies . Springer Science & Business Media. 2007. 978-0-387-73743-0. Ansell SM . 383. 17. Langerhans Cell Histiocytosis.
12. Web site: Full Members . 2023-09-27 . NACHO – North American Consortium for Histiocytosis . en.