Fluoroquinolone toxicity can potentially trigger or exacerbate Mast Cell Activation Syndrome (MCAS) due to its ability to directly activate mast cells through a receptor called MRGPRX2, leading to symptoms like histamine release and allergic-like reactions in susceptible individuals; this is considered a potential mechanism for a link between fluoroquinolone use and MCAS symptoms [12]. 

Mast Cell Activation Syndrome is not the same as Mastocytosis. Mastocytosis is the inappropriate proliferation of mast cells, whereas, Mast Cell Activation Syndrome is the inappropriate activation of mast cells. These are two very different diagnoses, although they are often confused as the same thing. 

Mast Cells are a type of white blood cell and part of your immune system. Mast cells are located all over your body, except in the retina and spinal cord. They respond to both everything inside and outside the body. And they tend to be in higher numbers in areas that interact with the outside environment, like the lungs, skin and gastrointestinal tract. Think of Mast Cells as the “guards at the gate,” protecting the castle. When a person without mast cell encounters an illness or virus (invader), the guards at the gate (mast cells), defend the person against the illness, and when the invader is defeated, will guards will retreat back to the castle. With Mast Cell Activation Syndrome, the immune system has been triggered (for various reasons) and the guards at the gate do not understand who is friend or foe. In that case, they attack everyone that tries to enter the castle. Think of MCAS as a cellular form of protection. When mast cells attack what they perceive as an invader, they release histamine and hundreds of other bio chemical mediators that create inflammation (this is called mast cell degranulation). When a person has a mast cell attack, they usually react immediately, in the sinuses, neck, throat, gut, etc.. Mast cells create an allergic symptoms by producing mediators.  

Mast cell activation syndrome only became a clinical diagnosis in 2016, which means it is still a syndrome that is not well understood and testing is poor at best. Testing for MCAS is often confused with testing for mastocytosis, which includes an elevated tryptase. This testing for mast cell is antiquated because we have thousands of mediators but we only have tests available for a dozen. Additionally, most mast cell patients have normal tryptase levels. This is because mediators are released transitorily - they are there, and then they are gone, but their biochemical effects go on for hours. So testing is basically useless. A good doctor will make a clinical diagnosis. Doctors who understand mast cell, also understand that tryptase is an antiquated way of diagnosing this syndrome. Instead, they will make a clinical diagnosis based on consensus 2x: aka a multi-system and multi-symptom issue.

Your mast cell related symptoms depend on which mast cells are triggered. that’s why your symptoms can vary so widely and may seem so strange and difficult to diagnose.