The MastAttack 107: The Layperson’s Guide to Understanding Mast Cell Diseases, Part 25

I answered the 107 questions I have been asked most in the last four years. No jargon. No terminology. Just answers.


33. What is the difference between primary and secondary disorders? How do you know if your disorder is primary or secondary?
• This is a case where we badly need better vocabulary for describing a phenomenon than these two words. The reason for this is because primary and secondary have an inherent numerical association – primary means first, secondary means second. We think that it means primary disorders happen first and secondary happen after. This isn’t always the case.
• A primary disorder does not mean the first disorder to be found. It also does not necessarily mean the disorder that causes other disorders. In this context, primary means only that the disorder arose irrespective of any other health issues, that it was always going to happen anyway.
• So let’s say you have a primary disorder, systemic mastocytosis. Now let’s say that you have another health issue. Whether you had cancer, a bad sunburn, or a broken toe, systemic mastocytosis was always going to happen to you. Or if you lived a charmed life and never had another health issue at all, even a runny nose. Systemic mastocytosis was always going to happen to you.
• We need to make a very, very important distinction here. Somewhere inside your cells was a seed that would later grow into systemic mastocytosis. However, sometimes that seed grows much faster because something else happens to you. People sometimes say “I got SM after I got pregnant”, or “I got SM after a bad car accident”. This isn’t really accurate. You were going to get SM at some point anyway. These are things that really activate mast cells so sometimes events like that can trigger mast cells so that you see the disease then for the first time.
• Clonal disorders are disorders where your body makes too many cells that don’t work correctly. Clonal disorders are almost always considered primary diseases. Clonal mast cell diseases are monoclonal mast cell activation syndrome, mastocytoma, mast cell sarcoma, and all forms of systemic mastocytosis and cutaneous mastocytosis. In all of these conditions, the body makes too many mast cells that do not function correctly.
• Now remember – primary does not mean first. It also does not meet only. You can have multiple primary diseases. You can have systemic mastocytosis and a genetic immunodeficiency. Both of those are primary. If you never had SM, you would still have the genetic immunodeficiency. If you never had the genetic immunodeficiency, you would still have SM. You can have multiple primary disorders.
Secondary disorders are disorders that do depend upon another health condition. Many disorders are secondary.
• For example, steroid induced diabetes is a classic example of a secondary disorder. If you take high dose steroids for too long, you develop diabetes as a result. But if you can get off the steroids, the diabetes resolves. You only had the diabetes because of the steroids. The diabetes was not always going to happen to you. It happened because of the steroids.
• When mast cell patients ask about primary and secondary diseases, they are almost always asking about mast cell activation syndrome. Mast cell activation syndrome is overwhelmingly considered to be a secondary disease. Many patients with MCAS have other diseases and MCAS is thought to be a reaction of the body to the stress and damage of the other diseases. Autoimmune diseases, connective tissue diseases, and even bad IgE allergies are commonly cited as the primary diseases that MCAS is secondary to.
• In a conversation with a world known authority on mast cell diseases, I was told that about 95% of MCAS is thought to be secondary. I also think that MCAS is almost always secondary, though I haven’t seen data to really feel solidly convinced of that.
The terms “primary MCAS” and “monoclonal mast cell activation syndrome” are usually used interchangeably. This is because monoclonal MCAS is clonal (too many broken cells) and clonal diseases are primary diseases.
• However, I am not personally convinced that there is no other primary form of MCAS. This is the same caveat as the previous point – there’s just not enough data. I do think that most MCAS patients have secondary disease. But those are just thoughts without evidence.
In idiopathic disorders, you don’t know why they happen. The same expert told me that idiopathic MCAS occurred in about 5% of cases. In these instances, the patients did not have any other diagnoses that were thought to cause secondary MCAS (and sometimes no other diagnoses at all).
• Let’s review.
• Primary disorders were going to happen to you at some point no matter what.
• Secondary disorders happen when your body reacts to something else happening in your body.
• Idiopathic disorders have no obvious cause.

This is an extremely confusing topic. Please ask questions in the comments if you have them.

For more detailed reading, please visit these posts:
The Provider Primer Series: Mast cell activation syndrome (MCAS)
The Provider Primer Series: Cutaneous Mastocytosis/ Mastocytosis in the Skin
The Provider Primer Series: Diagnosis and natural history of systemic mastocytosis (ISM, SSM, ASM)
The Provider Primer Series: Diagnosis and natural history of systemic mastocytosis (SM-AHD, MCL, MCS)