Constitutional symptoms of MCAS

Constitutional symptoms are any symptoms that affect the function of several systems at once.  They are often nonspecific and can be attributed to many causes, complicating diagnosis. For many people with MCAS, the constitutional symptoms present first and with the greatest frequency.

Fatigue and malaise (the feeling of being “out of it”) are the most common symptoms reported in MCAS patients.  While many patients with these symptoms remain functional, for some, it can be truly, severely disabling, with some patients sleeping for the majority of the day.  Dr. Afrin has referred to stories of “patients in their twenties acting like they are in their eighties.”  Chronic fatigue syndrome, in which patients have severe fatigue unrelated to exertion, not relieved by rest and unrelated to other medical conditions, has been tentatively linked to mast cell activation by Dr. Theoharides. 

I see a lot of discussion about whether or not fevers are part of MCAS.  It depends which researcher is reporting information.  Castells feels strongly that fevers are not part of MCAS symptomology, while Afrin and Molderings feel that they are.  They report that intermittent elevated temperatures are not unusual.  These temperatures are low-grade temperatures, with frank fever being quite rare.  MCAS patients often report constantly feeling cold, though chills and shaking is less common.

I know that one of the ways I can tell my mast cell disease is ramping up is by severe night sweats.  This is apparently common in most presentations of mast cell disease.  As such, many MCAS patients have severe, unprovoked sweating, often overnight, sometimes not.  Some patients report a circadian rhythm.  Furthermore, this sweating is often accompanied by swollen or tender lymph nodes.  When these two symptoms are taken together, usually infection or lymphoma is suspected.  Once these are ruled out, patients are often left with no relief for this frustrating symptom.

Some patients report lack of desire to eat.  Some report quickly feeling full (early satiety.)  In some of these patients, the root cause is a swollen spleen.  A minority of MCAS patients lose weight due to their disease.

Weight gain in MCAS patients is far more common than weight loss.  It often begins suddenly and progresses rapidly, in the absence of dietary or activity changes.  This is partially due to the fluid dynamics of edema due to mast cell activation.  Less often, weight gain is from ascites (free fluid in the abdomen) or serositis, inflammation of the serous tissues, including the pleura (tissue lining the lungs), pericardium (the compartment containing the heart and origination of the large vessels connecting to the heart) and the peritoneum (tissue lining the abdomen.) 

However, the gain in adipose (fat) tissue seems to be responsible for most of the persistent weight gain.  Some patients gain more than 50kg in a year despite significant caloric restriction and frequent exercise.  Many people (and their providers) often attribute their worsening symptoms to the gained weight.  Some people undergo bariatric surgery and despite initial losses, regain the weight, with no improvement of other symptoms.

Pruritis (itching) is very common in MCAS.  Its presentation is varied; episodic or constant; local or diffuse; migratory or not; tolerable or disabling.   

The hallmark of MCAS is that patients invariably present with a collection of “sensitivities.”  These include severe or bizarre reactions to virtually anything, including drugs, food and environemental triggers.  Environmental triggers can be due to the presence of common allergens, physical (such as heat), electrical (such as generation of electrical charge when brushing hair) and even osmotic.  Exposure to harmless microorganisms can cause severe reactions.  Summers are often difficult for MCAS patients due to heat and increased UV exposure, while spring and fall are difficult due to pervasive pollen.  Triggers can cause reactions when the patient touches, inhales or ingests them. 

Though less of a problem than heat, exposure to cold can trigger a hyperadrenergic response that will fuel mast cell activation.  Care must be taken to avoid temperature extremes on either end of the spectrum.

Drug sensitivities are often found to be due to an inactive ingredient in the formulation.  Compounding is an important tool for MCAS patients.  Lactose monohydrate and potato are common fillers for MCAS patients.  Reconstitution at time of use with water is also not uncommon.



Afrin, Lawrence B.  Presentation, Diagnosis and Management of Mast Cell Activation Syndrome.  2013.  Mast Cells. 

3 Responses

  1. Matthew February 7, 2016 / 1:47 am

    I have read a number of your blog entries and I think I’ve only commented a couple times. I was diagnosed with MCAS this past year. My prostaglandins are my biggest problem, and I am frequently hot and night sweats are FAR too common. I have noticed that during these episodes, particularly when I feel hot, my temp is hovering around 99.8-100.5, not techinically a fever, but my body temp USED to always be 98.5, unless I was actually sick with a bronchitis, etc.

    I guess I have a question, have you experienced a low-grade fever yourself?

  2. Dani April 10, 2016 / 5:34 pm

    I recently saw a Dr in Seattle, that is familiar with MCAS, he disagrees with Dr. Afrin about low grade fevers. I think it is related or caused by MCAS. Twice now when I have been feeling very ill, but not from an infection, I have gone to urgent care. Both times I had a low grade fever (but since I am normal about 97 or so it feels crazy hot to me) and one time they did a CBC & CMP and my monocytes were high, potassium low, protein high. I also went from shivering to completely flushed & burning. I did test positive for autoimmune urticaria with the Seattle Dr. but have not heard from him. His staff told me to stop my antihistamines, which was unnecessary & dangerous, but I noticed my so called TMJ pain came back while off my medications, which seems odd & makes sense at the same time! Thank you for your blog, sharing information & making it easy to understand!

  3. Matthew Hawn April 11, 2016 / 1:41 pm


    Misery loves company, they say! It’s good to know I’m not the only one who sometimes feels like I’m just burning up. No chills with a fever for me, at least not 99% of the time. My monocytes have been high in the past, too.

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