PMDD and MCAS: how they interact

MCAS here stands for Menstrual Cycle-Associated Syndrome, a term one group of researchers proposed for premenstrual symptoms linked to immune and growth-factor markers in the blood (CNS & Neurological Disorders Drug Targets, 2021). It isn't mast cell activation syndrome, a separate immune condition that happens to share the same initials.

Researchers diagnose MCAS when a woman's total score on the Daily Record of Severity of Problems (DRSP) chart during a full cycle sits above the 66th percentile, combined with a clear rise in symptoms during the week before her period (CNS & Neurological Disorders Drug Targets, 2021; Preprints.org, 2019).

PMDD is different. It's a recognized diagnosis in the DSM-5-TR and ICD-11, confirmed by doctors using at least five symptoms, one of them a mood symptom, tracked daily over at least two cycles.

Both frameworks use the same DRSP scale and look for the same pattern: symptoms rising before bleeding and easing afterward. MCAS adds something the DSM-5 doesn't: a proposed set of blood markers behind that pattern.

Yes, and that's built into the definition. Researchers require a measurable rise in DRSP scores during the week before a period, not just high symptoms all month (CNS & Neurological Disorders Drug Targets, 2021).

In the study behind this research, scientists measured blood levels of several chemokines, cell-signaling proteins involved in inflammation, in 41 women at four points across the cycle (Journal of Affective Disorders, 2020).

Women who fit the MCAS pattern had higher CCL2, CCL5, CCL11 and EGF than women who didn't. CCL2 alone explained about 39.6% of the variation in DRSP scores in that study (Journal of Affective Disorders, 2020).

Which marker mattered most changed by week. CCL2 predicted symptoms in the first two weeks of the cycle. CXCL10 was the strongest predictor in week three, and a mix of CCL2, CCL11 and CCL5 predicted week four (Journal of Affective Disorders, 2020).

This fits the broader PMDD picture. Hormone levels during this time are normal; some bodies react more strongly to the usual drop in estrogen and progesterone before a period (Schmidt et al., 1998; Dubey et al., 2017).

PMDD's prevalence is well studied. About 1.6% of women and girls in community studies confirmed the diagnosis with daily tracking, 3.2% across all confirmed-diagnosis studies, and 7.7% on a provisional diagnosis (Reilly et al., 2024, Journal of Affective Disorders).

MCAS doesn't have a population prevalence rate yet. The research behind it comes from one study of 41 women, measuring blood chemokines against DRSP scores (Journal of Affective Disorders, 2020). That's enough to support a biological pattern, not enough to say how many women would meet this case definition in general.

Because MCAS uses the same DRSP scale that PMDD research relies on, many women who'd qualify for a PMDD diagnosis likely also fit the MCAS pattern described in these papers. Both describe the same overlapping symptoms, one through a clinical lens and one through blood markers.

If your symptoms fit the PMDD pattern, more established care already exists through a PMDD diagnosis, regardless of whether MCAS research ever becomes a formal diagnosis.

There's no separate treatment guideline for MCAS, because it isn't a clinical diagnosis. The chemokine research points to what might drive symptoms; it hasn't produced a different treatment.

For PMDD, guidelines point to a few options a doctor might consider:

• SSRIs, which some people take only during the luteal phase
• Certain hormonal contraceptives
• Cognitive behavioral therapy (CBT)

None of these were tested against the specific chemokines named in the MCAS research above. They're still the best-supported options for the mood and physical symptoms both frameworks describe.

If you already have a diagnosed condition, like depression or anxiety, that worsens before your period but doesn't fully ease afterward, that's a different pattern called premenstrual exacerbation. PME needs its own treatment plan for the underlying condition, alongside anything that helps the premenstrual worsening.

A doctor decides what treatment fits your pattern, not a chemokine panel.

Whether you'd call it PMDD, MCAS or just something else, the days before your period call for something concrete.

Try this when a hard moment hits:

1. Leave the room if you're mid-argument, and say you need 20 minutes before continuing.
2. Breathe out for six counts, a few times, to slow your body down before you respond.
3. Write down what happened while it's fresh, including what you'd want to say once you're calmer.
4. Move your body for a few minutes, even a short walk, since physical symptoms like pain and fatigue are part of this pattern too.

Niyora is a PMS and PMDD support app. If you want somewhere to put the fight before you answer, Niyora's Moon lets you write what happened, see it from another side and draft a reply you can hold for 20 minutes.

None of this changes the underlying chemistry researchers are studying. It gives you something to do in the next ten minutes, which is often what the moment calls for.

Both frameworks rely on daily symptom ratings across a full cycle, not a memory of how last week felt.

The DRSP chart is the scale researchers used to define MCAS, and the one doctors use to confirm PMDD. Filling it out daily, for at least two cycles, gives you the pattern a doctor or researcher would actually look for.

What to log each day:

• Mood (irritability, sadness, anxiety, rejection sensitivity)
• Physical symptoms (pain, fatigue, bloating, sleep)
• Where you are in your cycle (day count from your last period)

If you're not sure whether this pattern fits you at all, this quiz is a quick starting point before two months of daily tracking.

Once you have that record, getting a PMDD diagnosis starts with bringing it to a GP or gynecologist.