Rosai-Dorfman syndrome is a rare disorder where the body produces too many of a particular type of white blood cell, leading to swollen lymph nodes and sometimes affecting other organs throughout the body.
Understanding Rosai-Dorfman Syndrome
Rosai-Dorfman syndrome, also known as Rosai-Dorfman disease or RDD, is a rare condition involving the abnormal buildup of histiocytes, which are a type of white blood cell that normally helps your immune system fight off infections. When these cells multiply excessively, they can accumulate in different parts of your body, most commonly in lymph nodes but also in other tissues and organs. The condition was first identified in 1969 by two pathologists, Juan Rosai and Ronald Dorfman, who studied several children with massive enlargement of their lymph nodes along with other symptoms.[1][2]
In recent years, scientists have made important discoveries about this condition. Researchers have identified cancer-causing genetic changes, called mutations, in the MAP kinase pathway in about 50% of cases with RDD. Because of these findings, the World Health Organization recognized RDD as a type of blood cancer in 2022. However, despite this classification, RDD is usually not life-threatening, and many patients do not require treatment at all.[2]
The condition is also called sinus histiocytosis with massive lymphadenopathy, a name that describes its most common feature: significant swelling of lymph nodes caused by histiocyte accumulation in the spaces within them. It belongs to a broader group of disorders called non-Langerhans cell histiocytoses, which are conditions involving abnormal buildup of histiocytes that are not of the Langerhans cell type.[1]
Epidemiology: Who Gets Rosai-Dorfman Syndrome
Rosai-Dorfman syndrome is extremely rare worldwide. About 1 in every 200,000 people develops RDD, which means that in the United States, approximately 100 new cases are diagnosed each year. The condition occurs across the globe and affects people of all backgrounds, though certain patterns have been observed in different populations.[1]
The disease mainly affects children, teenagers, and young adults, with most diagnoses occurring around age 20. However, cases have been recorded in people ranging from very young children to individuals in their 70s. In one study of 64 patients seen at a major medical center, the median age at diagnosis was 50 years, with ages ranging from 2 to 79 years, showing that the condition can truly affect people at any stage of life.[3]
Interesting demographic patterns emerge when looking at the different types of RDD. When the disease affects the lymph nodes (called nodal RDD), it occurs most frequently in people of African descent who are male. In contrast, when the disease affects the skin (called cutaneous RDD), it is typically diagnosed in people of Asian descent who are female. Cutaneous RDD mostly affects people in their 20s, 30s, and 40s.[1]
Despite these patterns, the exact incidence of RDD cases worldwide is not fully known. The condition seems to affect equal numbers of males and females overall when all forms of the disease are considered together. It can affect both children and adults, and because this disease is so rare, no large-scale studies have been performed to establish precise population-level statistics.[2]
Causes of Rosai-Dorfman Syndrome
The exact cause of Rosai-Dorfman syndrome remains unknown, which is one of the frustrating aspects of this rare condition. Researchers have considered many possibilities over the years, including viral infections, bacterial infections, environmental factors, and genetic causes, but no single clear trigger has been identified that explains why some people develop this overproduction of histiocytes.[2]
Several infectious agents have been studied as possible causes. Researchers have investigated whether viruses such as Epstein-Barr virus, parvovirus B19, and human herpesvirus 6 might trigger the condition. Bacteria like Klebsiella and even infections like tuberculosis have also been considered. However, none of these infectious agents has been definitively proven to cause RDD, and many patients with the condition show no evidence of these infections.[5]
The most significant recent discovery about what causes RDD involves genetic changes at the cellular level. In the last decade, scientists have identified that cancer-causing genetic mutations in the MAP kinase pathway are present in approximately 50% of cases with RDD. This pathway is important for controlling cell growth and division. When mutations occur in this pathway, cells may begin to multiply excessively. Similar mutations have also been found in related conditions like Erdheim-Chester disease and Langerhans cell histiocytosis, suggesting these disorders share some underlying biological mechanisms.[2]
Some researchers have proposed that inflammation might play a role in the development of RDD. One theory suggests that monocytes (another type of white blood cell) recruited to areas of inflammation could produce macrophage colony-stimulating factor, which then leads to a complex chain of signals that results in the abnormal histiocyte accumulation characteristic of the disease.[5]
Risk Factors
Because the cause of Rosai-Dorfman syndrome remains largely unknown, identifying specific risk factors that increase a person’s chance of developing the condition is challenging. Unlike many other diseases where clear risk factors such as smoking, diet, or lifestyle habits can be identified, RDD does not appear to have obvious preventable risk factors.
The age-related pattern suggests that being a child, teenager, or young adult may represent a period of increased susceptibility, though cases certainly occur in older adults as well. The demographic differences observed in different forms of the disease—with nodal disease more common in males of African descent and cutaneous disease more common in females of Asian descent—suggest that genetics and ethnicity may play some role, though the exact mechanisms remain unclear.[1]
There is no evidence that behaviors, habits, or environmental exposures that people can control increase the risk of developing RDD. The condition is not contagious and cannot be spread from person to person, even though researchers have investigated whether infectious agents might trigger it. Similarly, there is no evidence that lifestyle factors such as diet, exercise, occupation, or geographic location meaningfully influence the risk of developing this rare disorder.[2]
Symptoms and How They Affect Patients
The symptoms of Rosai-Dorfman syndrome vary widely depending on where the excess histiocytes accumulate in the body. Some people experience mild symptoms or even no symptoms at all, while others may have more severe manifestations if the histiocytes prevent an organ from functioning correctly. The disease can present in two main forms: classical (nodal) disease affecting lymph nodes, and extranodal disease affecting tissues and organs beyond the lymph nodes.[1]
In classical nodal Rosai-Dorfman disease, the most common symptom is painless, swollen lumps on both sides of the neck. These represent enlarged lymph nodes filled with excess histiocytes. The swelling can be quite dramatic, which is why the condition was originally called “sinus histiocytosis with massive lymphadenopathy”—the lymph nodes can become very large. While neck lymph nodes are most commonly affected (occurring in about 87% of cases in one large registry), lymph nodes in other parts of the body can also swell, including those in the armpits, groin, and the center of the chest.[1][5]
Many patients with nodal disease notice only the swelling and feel otherwise well. However, some people also experience additional symptoms that suggest the body is responding to the abnormal cell buildup. These can include fever, which may come and go without an obvious cause; pale skin resulting from anemia (a condition where there aren’t enough red blood cells to carry oxygen); fatigue that makes it hard to complete normal daily activities; night sweats that soak through bedclothes; a runny nose; and unexplained weight loss.[1]
About 40% of people with RDD have excess histiocytes in sites other than lymph nodes, a condition called extranodal disease. The skin is the most common extranodal site affected, occurring in approximately 52% of patients overall. When the skin is involved, patients typically develop nodules or lumps under the skin that can occasionally be itchy and painful. These skin manifestations can appear on various parts of the body.[2][3]
Other organs and tissues that can be affected by extranodal RDD include the nasal cavities and sinuses, where histiocyte buildup may cause breathing difficulties or chronic sinus symptoms; the eyes and eyelids, potentially affecting vision or causing swelling around the eyes; bones, which can lead to pain or structural problems; the salivary glands, affecting saliva production; and the central nervous system (brain and spinal cord), which is particularly concerning as it can affect neurological function.[1][4]
In rarer instances, RDD can affect internal organs such as the kidneys, lungs, liver, heart, breast, and digestive tract. When these organs are involved, symptoms relate to the specific organ affected. For example, lung involvement might cause shortness of breath or cough, while kidney involvement could affect how well the kidneys filter waste from the blood.[4]
In a study of 64 patients, the most common presentation was subcutaneous masses (appearing in 40% of patients), and among all patients, only 8% had classical nodal-only disease, while 92% had extranodal disease. Of those with extranodal disease, 67% had disease only outside the lymph nodes, while others had both nodal and extranodal involvement. This shows that the disease behaves very differently in different people.[3]
Prevention
Given that the cause of Rosai-Dorfman syndrome remains unknown and no clear risk factors have been identified, there are currently no known ways to prevent the condition from developing. Unlike some diseases where lifestyle modifications, vaccinations, or avoiding certain exposures can reduce risk, RDD appears to arise spontaneously without identifiable triggers that people can avoid.
Because approximately half of RDD cases involve genetic mutations in the MAP kinase pathway that occur during a person’s lifetime rather than being inherited, these cannot be prevented through screening of family members or genetic counseling in the traditional sense. The mutations are acquired rather than inherited, so they are not passed down through families in predictable patterns.[2]
There are no screening tests recommended for early detection of Rosai-Dorfman syndrome in the general population because of how rare the condition is. Similarly, there are no supplements, dietary changes, or lifestyle modifications that have been shown to prevent its development or reduce the risk of someone getting the disease.
For people who have been diagnosed with RDD, preventing complications or recurrence involves working closely with healthcare providers to monitor the disease and determine if and when treatment is needed. Because RDD is usually not life-threatening and many patients do not require treatment, careful observation may be the most appropriate approach for some individuals.[2]
Pathophysiology: What Happens in the Body
Rosai-Dorfman syndrome involves fundamental changes in how the immune system functions at the cellular level. The condition centers on the abnormal behavior of histiocytes, specialized white blood cells that normally play an important protective role in the body’s defense against germs and infections. Understanding what goes wrong requires looking at both the cells themselves and what they do when they accumulate in excess.[1]
In healthy individuals, histiocytes circulate through the body and lymph system, watching for signs of infection or disease. They can engulf and destroy bacteria, viruses, and other foreign materials—a process that helps keep you healthy. However, in Rosai-Dorfman syndrome, something triggers these cells to multiply excessively and accumulate in lymph nodes or other tissues, leading to the physical swelling and symptoms patients experience.
One of the distinctive features of RDD at the microscopic level is a phenomenon called emperipolesis. This unusual term describes what happens when intact, viable cells—particularly lymphocytes (another type of white blood cell), plasma cells, and neutrophils—become trapped inside the cytoplasm (the internal fluid) of the abnormal histiocytes. When pathologists examine tissue samples under a microscope, they can see these cells living within the histiocytes, almost as if the histiocytes have swallowed them whole but kept them alive. This is different from the normal process where immune cells destroy what they engulf. Emperipolesis is one of the hallmark features that helps doctors confirm a diagnosis of RDD.[5]
The histiocytes in RDD have specific characteristics that can be identified through special staining techniques called immunohistochemistry. When tissue samples are treated with different stains, the abnormal histiocytes light up positive for certain markers including S100, CD68, and CD163, but they are negative for CD1a. This staining pattern helps doctors distinguish RDD from other similar conditions that also involve histiocyte accumulation but have different staining patterns.[1][5]
At the genetic level, researchers have discovered that about 50% of RDD cases involve mutations in the MAP kinase pathway, also called the MAP-ERK pathway. This pathway is a chain of proteins inside cells that communicate signals from the cell surface to the nucleus, controlling important processes like cell division, differentiation, and survival. When mutations occur in genes like MAP2K1 or others in this pathway, they can cause cells to receive constant “grow and divide” signals even when they shouldn’t, leading to the excessive proliferation of histiocytes seen in RDD.[2][3]
When histiocytes accumulate in lymph nodes, they expand the spaces within the nodes, called sinuses, leading to the massive swelling that gives the condition one of its names. This physical expansion can affect how the lymph node functions in filtering lymph fluid and mounting immune responses. In extranodal sites, the accumulation of histiocytes can directly interfere with organ function depending on where they collect and how much space they occupy. For instance, histiocytes in bone can affect bone structure, while those in the brain can compress neural tissue.[1]
Some research suggests that inflammatory signaling molecules called cytokines, particularly interleukin-6 (IL-6), may play a role in RDD. Studies have found that some patients with active RDD have elevated levels of IL-6, and these levels normalize after successful treatment. IL-6 is a messenger molecule that can promote inflammation and stimulate immune cell production and activity. This has led some researchers to explore treatments that target IL-6 signaling.[11]
The disease can behave very differently in different people because of variations in where the histiocytes accumulate, how many cells are involved, and possibly whether genetic mutations are present. Some patients experience spontaneous remission, where the excess histiocytes gradually disappear on their own without treatment, suggesting the body can sometimes correct the abnormal cell growth naturally. Others have progressive disease that requires intervention. Understanding these variations remains an active area of research.[2]
