SALT LAKE CITY, UT — Mast cell activation syndrome (MCAS) may be an overlooked yet potentially treatable contributor to the symptoms of chronic fatigue syndrome/myalgic encephalomyelitis (ME/CFS), say physicians who specialize in ME/CFS and its manifestations.

The subject was discussed during a 2-day clinician summit held March 2 to 3, 2018, during which 13 panelists met to begin developing expert consensus guidance for primary care and specialist physicians for the management of the complex multisystem illness ME/CFS, and to recommend research priorities.

"ME/CFS is a descriptive diagnosis of a bunch of symptoms, but it says nothing about what's causing the symptoms, which is probably part of the reason it's so hard for it to get recognition. So, the question becomes, What other pathology is driving this illness and making the person feel so ill? I think mast cell activation is one of those drivers, whether cause, effect, or perpetuator, I don't know," internist David Kaufman, MD, who practices in Mountain View, California, told Medscape Medical News.

MCAS is a recently described collection of signs and symptoms involving several different organ systems, that, as with ME/CFS itself, do not typically cause abnormalities in routine laboratory or radiologic testing. Proposed diagnostic criteria were published in 2010 in the Journal of Allergy and Clinical Immunology.

Kaufman first learned about MCAS about 5 years ago from a patient who introduced him to the published work of mast cell expert Lawrence Afrin, MD. "I spoke to him and then I started looking for it, and the more I looked, the more I found it," Kaufman said, estimating that he has identified MCAS in roughly half his patients who meet ME/CFS criteria.

Indeed, summit panel member Charles W. Lapp, MD, who recently retired from his ME/CFS and fibromyalgia practice in Charlotte, North Carolina, told Medscape Medical News, "I see a lot of this. I think it's one of the many overlap syndromes that we've been missing for years."

Another panel member, New York City ME/CFS specialist Susan M. Levine, MD, also said she sees MCAS frequently. "I suspect 50% to 60% of ME/CFS patients have it. It's a very new concept."

In Levine's experience, MCAS often manifests in patients being unable to tolerate certain foods or medications. "If we can reduce the mast cell problem, we can facilitate taking other drugs to treat ME/CFS," she said. However, she also cautioned, "It's going to be a subset, not all ME/CFS patients."

Clinical Assessment and Laboratory Testing

As discussed at the summit, for patients who meet ME/CFS criteria, the next step is to drill down into individual patients' symptoms and address treatable abnormalities. Investigation for MCAS may yield such findings among those who exhibit episodic symptoms consistent with mast cell mediator release affecting two or more of the following areas:

Skin: urticaria, angioedema, flushing

Gastrointestinal: nausea, vomiting, diarrhea, abdominal cramping

Cardiovascular: hypotensive syncope or near syncope, tachycardia

Respiratory: wheezing

Naso-ocular: conjunctival injection, pruritus, nasal stuffiness

Symptoms can wax and wane over years and range from mild to severe/debilitating. It is important to ask about triggers, Kaufman advised. "The patient is usually aware of what makes them feel worse."

Routine laboratory assessments include complete blood count with differential, complete metabolic panel, magnesium, and prothrombin time/partial thromboplastin time.

More specific laboratory testing can be tricky, as the samples must be kept cold. These include serum tryptase, chromogranin A, plasma prostaglandin D2, histamine, heparin, a variety of random and 24-hour urinary prostaglandins, and urinary leukotriene E4.

For patients who have had a prior biopsy, the saved sample can be stained for mast cells.

Kaufman said that initially after he learned about MCAS, he would only run the laboratory tests in patients with suggestive clinical history, such as food sensitivities/triggers, rashes, hives, temperature intolerance, or chemical sensitivities. "But ultimately, I had patients [for whom] I couldn't figure out what was going on; I would check, and started finding positives in patients I wasn't suspicious of."

So, now he just tests for it in all his patients with ME/CFS. "It's bigger than allergy," he remarked.

Treatment May Ease Some ME/CFS Symptoms

Treatment of MCAS involves trigger avoidance as possible; H1 receptor antagonists such as loratadine, cetirizine, or fexofenadine (up to double the usual doses); H2 histamine receptor antagonists including famotidine or ranitidine; and mast cell membrane-stabilizers such as cromolyn sodium. Slow-release vitamin C can also help in inhibiting mast cells.

Over-the-counter plant flavonoids such as quercetin also may be helpful, typically at high doses (up to 1000 mg three times daily). "There's a long list of medications that either quiet down mast cell activation or block the receptor," Kaufman noted.

But despite that, without controlled trials, it is difficult to determine the exact clinical effects of blocking mast cells, especially as these patients tend to be taking many other medications. And in the context of ME/CFS, the extent to which suppressing mast cell activity addresses the core symptoms of fatigue, postexertional malaise, orthostatic intolerance, and cognitive dysfunction is unclear.

Kaufman noted, "I think treatment clearly helps with the fatigue because they're not reacting to everything. It improves gastrointestinal symptoms, so they can eat better.... I have seen [postural orthostatic tachycardia syndrome] improve, but I have to say I also give meds for dysautonomia, so I can't be sure."

Lapp said that in his experience, "[Patients with ME/CFS] aren't cured, but do get better. [Blocking mast cell activity] gets rid of dizziness, fatigue, nausea, and light sensitivity."

Levine pointed out, "We're just at the beginning of identifying this patient subset and thinking what makes sense to try.... One thing that's sure is that the drugs are pretty safe," she said, adding that when it comes to working up patients with ME/CFS for MCAS, "There only seem to be good things that can happen."

Kaufman, Lapp, and Levine have disclosed no relevant financial relationships.

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