Autoinflammatory diseases are a relatively new category of illnesses caused by disorders of one arm of the immune system. Many of these diseases are characterized by recurrent fevers, rash, chest and abdominal pain, and evidence of systemic inflammation on blood tests; these manifestations often mimic infectious or other illnesses, and it may take several years for the diagnosis to be made.
Most autoinflammatory diseases are genetic (inherited), start in childhood, and persist throughout adult life. These diseases are often present in several members of a family. Other autoinflammatory diseases appear to be acquired, perhaps due to the interplay of genetic and environmental factors, and can present at any time during childhood or adulthood.
The list of autoinflammatory diseases continues to grow every month. Here is a list of the autoinflammatory diseases as they stand so far:
When I was little, I used to get a lot of fevers. With my fevers, I would develop pain in one or both of my ears, and I felt so drained that I just wanted to be left alone to watch TV (or play Atari). If my fever spiked in the middle of the night, my parents would soak me in a tub of lukewarm water to lower my temperature (how I hated those baths!). On the following day, I would visit my pediatrician, who would invariably diagnose me with an ear infection. He prescribed a delicious bubble-gum flavored antibiotic that my parents kept at the top shelf in the refrigerator (out of my reach so I wouldn’t overdose). I’m not sure if it was the taste or the active ingredient, but this antibiotic always made me feel better. After what seemed like the millionth episode of fever, my pediatrician recommended that I get tubes in my ears, and the episodes of fever and ear pain subsided.
Recurrent infections, like those I had when I was a child, are the most common cause of frequent fevers in children. Usually, these infections are due to viruses, such as the ones that cause the common cold. Children with colds often develop symptoms attributable to the virus, including a runny nose, nasal congestion, or cough. Multiple infections, one after the other, are especially common in children attending daycare or school, where they trade viruses like I used to trade baseball cards with my friends. When I see these the worried parents of these children in my office, I have to remind them that it is normal for a child to have 9-12 colds every year. Fortunately, these children continue to grow and gain weight without difficulty, and they are healthy between episodes. “As your child grows,” I tell the parents, “her immune system will become better at fighting infections, and the frequency and severity of fevers will diminish.” Aside from stressing the importance of hand washing among all family members, there is not much that can (or needs) to be done about these episodes.
However, if the episodes do not clearly match the above description, other diagnoses should be considered. In this post, I will provide some tips that may help parents and physicians recognize a rare cause of fever in children: autoinflammatory diseases. The most common autoinflammatory disease in children is called PFAPA, which stands for Periodic Fevers, Aphthous stomatitis (canker sores or oral ulcers), Pharyngitis (sore throat) and Adenitis (enlarged glands in the neck). This disease usually presents in children less than 5 years of age, and causes episodes of fevers in addition to the features that make up the name of the disease (oral ulcers, sore throat, enlarged glands in the neck). The fever usually lasts about 4 days, and it recurs at regular intervals, usually every month. What is unique about PFAPA is that parents can usually predict when the child is “due” to get ill. The episodes of fever are so regular as to be predictable. This regularity is rare in most other diseases. PFAPA is commonly misdiagnosed as frequent Strep infections, and testing for Strep throat is usually negative. Patients do not readily respond to antibiotics, although their symptoms can disappear with one dose of steroids.
Another clue that the child may have an autoinflammatory disease is that all of the episodes of fever look alike. For example, if the child always develops abdominal and joint pain with the fevers, then he may have familial Mediterranean fever (FMF). If, in addition to fever, she always develops a painful rash, muscle pain, and red eyes, then she may have TNF-receptor associated periodic fever (TRAPS). If he develops fevers, rashes, and joint pain after exposure to cold weather, then the child may have familial cold-induced autoinflammatory syndrome (FCAS).
The length and frequency of fever, associated symptoms, and age at which the fevers began can help differentiate between these (and other) autoinflammatory diseases. Thus, it is very helpful to keep a fever diary, specifying the characteristics of each episode. Because many of these autoinflammatory diseases are inherited (genetic), there is often a history of other family members having similar symptoms. In addition, it is important to note that some autoinflammatory diseases are more common in people of certain ethnic backgrounds, such as FMF in Sephardic Jews, Turks, and Armenians.
In addition to autoinflammatory diseases, there are some features of recurrent fevers that should warrant a closer look by a child’s pediatrician. These include prolonged episodes of fever (more than one week), recurrent fever without symptoms attributable to a viral infection, difficulty growing or gaining weight, or if the child does not return to his baseline between episodes. Other causes of fever that should be considered in these instances include:
Immunodeficiencies: problems in the immune system that makes the child more susceptible to infections
Anatomic and metabolic abnormalities: abnormalities in certain organs that make them more prone to infections (like my ears), or diseases such as cystic fibrosis
Inflammatory bowel disease: inflammation of the intestines
Cancer: such as leukemia or lymphoma
With this knowledge, parents and pediatricians alike can help distinguish between the majority of children that develop recurrent fevers because of frequent viruses, from causes which may require additional workup or treatment.
Last week during our weekly physician conference, I discussed a patient with an autoinflammatory disease. An elderly male, he had a history of recurrent fevers, hives, and elevated inflammatory markers, which had gone untreated for many years. Eventually, he developed renal amyloidosis (accumulation of amyloid fibers in the kidney causing kidney failure), and was finally referred to rheumatology clinic for further evaluation. Although he had many of the classic signs and symptoms of an autoinflammatory disease, his physicians had not recognized it. Even at the conference, some physicians were unaware of these group of diseases.
Autoinflammatory diseases are a newly described set of illnesses that cause systemic inflammation due to problems in the innate immune system. The innate immune system includes several types of white blood cells such as neutrophils, macrophages, and natural killer cells. These cells are the first responders to an infection because any one of them is able to recognize common patterns that are present in many types of pathogens (such as the cell wall in a bacteria). In response to a pathogen, these cells secrete inflammatory molecules (cytokines) that alert other cells of the immune system and get the body ready to fight.
Autoinflammatory diseases are often caused by genetic mutations within the cells of the innate immune system. These mutations lead to episodes of unprovoked activation of the immune system (production of inflammatory cytokines, recruitment macrophages, neutrophils, etc). In a sense, the body acts as if an infection were present, even when there is none. This is why many of the symptoms of autoinflammatory diseases–such as fever, rashes, joint pain–mimic infections, and why these diseases are often difficult to diagnose. The best characterized autoinflammatory condition is Familial Mediterranean Fever, which causes recurrent, brief attacks (12 to 72 hours) of fever, abdominal pain, chest pain, joint pain, and evidence of inflammation on blood tests.
In contrast, autoimmune diseases arise from problems in the adaptive (humoral) immune system. The adaptive immune system is more sophisticated than the innate, and is made up of very specialized B cells and T cells. Each B and T cell in our body is unique, and is only able to recognize a specific pathogen. Thus, it takes much longer for a B or T cell to recognize that a pathogen has invaded the body. However, once the pathogen is identified, the cell divides and multiplies, leading to a very effective and direct attack on the pathogen. B cells also produce antibodies, which help to neutralize the pathogen. Unlike the innate immune system, the humoral immune system develops “memory,” so that it is better able to fight the pathogen when it reencounters it in the future.
In autoimmune diseases such as lupus, the B and T cells of the adaptive immune system lose the ability to differentiate self from non-self. That is, they start seeing specific organs in the body as foreign (almost as if they were pathogens!), and thus begin to mount an attack against those organs, often leading to organ damage or destruction. In lupus, B and T cells often target the kidney, lungs, or heart, often leading to damage or destruction of these organs. However, autoimmune diseases can target almost any organ in the body. For example, in multiple sclerosis, cells attack the brain. In rheumatoid arthritis, the joint is the target organ. In pemphigus, the body attacks the skin. For reasons that are still unknown, autoimmune diseases more often affect women, whereas autoinflammatory diseases usually affect both sexes equally.
In the end, I think my patient may have had Muckle-Wells syndrome, an autoinflammatory disease caused by mutations in the NLRP3 gene. Autoinflammatory disorders are are still underdiagnosed and poorly understood. It seems like every month, a new autoinflammatory disease is discovered (take a look at this week’s New England Journal of Medicine). Furthermore, various pathways that are abnormal in autoinflammatory diseases have been implicated to play a role in more common diseases such as heart disease and diabetes. Thus, by understanding these rare disorders, we may gain a better understanding of diseases that afflict millions of people throughout the world.
Uncovering the mysteries of autoinflammatory diseases and other rheumatic illnesses.