A Disease Sometimes Confused With Ankylosing Spondylitis

                        (And Will Make You Grateful That You Only Have Ankylosing Spondylitis)

There is a disease so rare that it only strikes one out of 1.6 million people in the world. Only 800 patients are known to have the disease. It’s so rare, that it is often misdiagnosed. In its early stages, it has been misdiagnosed as Ankylosing Spondylitis (1). The majority of individuals who suffer from this disease are bedridden by the time they reach their thirties. Therefore, it strikes an individual early in life, just as Ankylosing Spondylitis often becomes diagnosed while a person is relatively young.  In fact, symptoms of this disease can begin to manifest as young as 5 years of age or less.


The primary symptoms?  Severe pain, swelling, stiffness, and eventually fusing. A person who is familiar with the symptoms of Ankylosing Spondylitis can begin to see why these early symptoms might be confused with AS, an inflammatory disease which also causes severe pain, swelling, stiffness and can lead to eventual fusing. But there are some very, very significant differences between this disease, known as FOP (fibrodysplasia ossificans progressiva), and Ankylosing Spondylitis.


While Ankylosing Spondylitis can lead to fusing of the vertebrae of the spine, resulting in a condition sometimes referred to as “bamboo spine”, FOP always (not sometimes) leads to fusing that involves, not just the spine, but all the muscles, ligaments and tendons of the body. In effect, the body becomes completely immobile and transformed into a statue of bone. Eventually, the patient is imprisoned in their own bones.


Many people do not realize that our muscles are considered organs, and so are our bones. Therefore, FOP is the only disease known where one organ is converted into another organ.


While Ankylosing Spondylitis does have a number of various treatments available on the market, including natural management strategies that involve diet modification, there are no known treatments available for FOP, as of the time of the writing of this article, other than steroids which can sometimes provide temporary relief from pain and inflammation during a flare up. Removal of the excess bone, unfortunately, only seems to provoke more bone to grow back, worsening the condition. Likewise, because the condition is often misdiagnosed, sometimes treatments that are commonly prescribed for AS or other conditions are given to these patients, making their condition worse. Diagnostic tests that cause even mild trauma, such as injections, or biopsies, accelerate the process also. Of course, any other kind of trauma, from falls, bruises or injuries, also accelerate the disease. For unknown reasons, bacterial or viral infections also can cause flare ups that cause the disease to progress more rapidly.


Both conditions have been linked to specific genes. People who possess the gene or genes linked to Anklylosing Spondylitis, however, may never develop the disease. An external environmental factor is believed to be necessary in order to trigger, or activate, said gene(s). However, FOP is considered a congenital disorder. In the majority of cases, it is caused by a spontaneous mutation that occurs at the time of conception. Therefore, individuals are born with the disease. The mutation can be passed on to a second generation in a rare number of cases. Most individuals with the disorder choose to not have children. Overall, it is the rarest congenital disorder on the planet. Still, 800 people with this disease is 800 too many to have to suffer with it.


The disease is apparent at birth, with a malformed big toe. However, this sign is often ignored or overlooked until a person begins to develop serious symptoms later on, often before 10 years of age. Typically by the time they are teenagers, they cannot fully raise their arms. Their first flare up of the disease usually presents before the age of 10, and progresses from the top of their body downward. Their jaws become fused, making speech and eating difficult. As muscles surrounding the lungs convert into bone, the expansion of the lungs are restricted, causing breathing complications. The diaphragm muscle, however, is not affected by the process, and neither are the cardiac muscles, nor the smooth muscles (such as the stomach and intestines), nor the tongue.


One person who suffered from FOP, Harry Eastlack, donated his body to science at the time of his death. He lived from 1933-1973, and began experiencing symptoms at the age of 10. By the time he passed away, his body had completely ossified. The only part of his body he could still move were his lips. His skeleton is kept at the Mutter Museum in Philadelphia, and it has proved to be an invaluable source of information for those studying the disease.


While Ankylosing Spondylitis is an inflammatory autoimmune type of Arthritis, FOP is considered a connective tissue disorder. In addition to sometimes being confused with Ankylosing Spondylitis, the disease is also misdiagnosed sometimes as cancer or fibrosis. Often biopsies are ordered because of the painful, swollen lumps that present, and the biopsies lead to a worsening of the condition.


The average age of survival with FOP is about 40 years. However, this can be decreased by trauma. By contrast, an individual with Ankylosing Spondylitis can live out a full lifespan with proper management, although it is believed that the lifespan is reduced somewhat. This has not been proven, nor has a figure to calculate the average reduction been determined by studies attempting to do so.


In summary, here are some of the main differences between Ankylosing Spondylitis and FOP:


1. With FOP, the big toe is characteristically malformed. Not so with AS.


2. With FOP, there are tumor-like swellings over an affected area during a flare up. Not so with AS.


3. FOP results in ossification of all muscles, ligaments, and tendons (with a few exceptions), due to excess bone formation, resulting in a fusing of the skeleton. With AS, only in the most severe cases (or cases of mismanagement) does the disease sometimes result in ossification of connective tissues between the vertebrae, due to excess bone formation, resulting in a fusing of the spine.


4. AS is an autoimmune inflammatory arthritis. FOP is a congenital disease.


5. The genes associated with FOP are completely different from the genes associated with AS. Also, patients who have FOP rarely inherited their condition from their parents. In most cases, it is a spontaneous mutation. However, AS is known to run in families.


6. The typical lifespan of an individual with FOP is 40 years. The typical lifespan of an individual with AS is thought to be reduced, but not significantly enough where a numerical figure has been determined, despite efforts to calculate such a figure.


7. There are known treatment regimes that help manage the symptoms of AS, including diet changes, exercises, natural products, and a variety of conventional pharmaceutical medications. However, in the case of FOP, there are no known medications that halt the disease or slow down the progression of the disease. Only steroids are sometimes prescribed during a flare up, to ease the inflammation, swelling and pain.


8. FOP is considered a rare disease, with only about 800 known cases worldwide, at the time of this writing. However, AS is not a rare disease, despite the tendency of it often being confused as such. In the United States, a disease is classified as rare if it affects less than 200,000 Americans at any given time. According to the Centers for Disease Control and Prevention’s National health and Nutrition Examination Survey (NHANES), almost 3 million people in the United States alone may have AS and related conditions. This is a conservative figure because there are a number of people with AS who are undiagnosed or misdiagnosed.




Exciting progress was made when a gene was identified as being associated with FOP. The result of this discovery could lead to a treatment strategy, although it might be many years before such a treatment is available. Other trials, however, are underway for other possible treatments and may be available in the years to come.



1. Thete SS, Pawar ED, Bafna G, Pawar P. Fibrodysplasia ossificans progressiva diagnosed as ankylosing spondylitis: A case report. International Journal of Case Reports and Images 2014;5(1):62–65.

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