People with rare diseases at generally referred to as zebras. In medical school, doctors are trained that when you hear hoofbeats, think horses, not zebras. This means that you should consider all the more likely causes before jumping to a rarer diagnosis. However, there are some people in this world for which the title of zebra still doesn't work. I am not proud of it, but it is the truth.
I am a unicorn. Now, I more than likely have a variant of stiff person syndrome (SPS) that is not yet named, but has the components of several of the named variants. While there is a recognized spectrum, there is really only one true name for all conditions on the spectrum, which as you can imagine, can make things difficult to name/identify.
For me, my SPS is pediatric onset with antibodies against GAD65 and amiphyphisin in serum and CSF. Less than 5% of cases have antibodies against amphyphisin, which generally suggests the presence of some kind of cancer, usually of the chest, which I also don't have. About 60% of all SPS cases have antibodies against GAD65, while about 40% will be diagnosed without the presence of GAD65.
Pediatric onset, antibodies associated with cancer (without the cancer), antibodies in both serum and CSF. Yep, totally a unicorn now. I have yet to find a case study of someone like me and I've been scouring medical school databases and literature for a while now. I know other people have been looking as well.
So while there aren't many out there, it is important to acknowledge that these so-called medical unicorns do exist and they struggle with their health just as much and maybe even more than zebras due to a lack of proper knowledge and medical treatments available.