Thinking at Half Speed

If you live with a chronic condition, someone has probably handed you a questionnaire about fatigue at some point. There are several recognised scales in clinical use, and they’re not all the same thing.

Fatigue Severity Scale (FSS) — nine statements, each scored 1 to 7. Developed in 1989 for MS and lupus research. Designed primarily to distinguish fatigued patients from healthy controls. A mean score above 4 is considered clinically significant. Short, simple, no cognitive heavy lifting required.

Modified Fatigue Impact Scale (MFIS) — 21 items covering physical, cognitive, and psychosocial dimensions separately. More detailed and more informative about where fatigue is hitting you hardest, but considerably more demanding to complete.

Chalder Fatigue Scale — 11 items, splits physical and mental fatigue. Widely used in CFS/ME research. Has a binary version for clinical caseness as well as a scored version.

PROMIS Fatigue — part of the NIH’s standardised patient outcomes system. Well validated, can be done as a short form, designed to work across conditions rather than being disease-specific.

We chose the FSS. Not because it’s the most informative — it isn’t — but because it’s the least demanding to complete. Nine questions, straightforward statements, no sub-scales to navigate. When your cognitive capacity is limited and your energy is rationed, that matters. The questions were put one at a time because reading all nine and holding them in mind long enough to score them was too much.

The score was 7.0. Maximum possible. Every question.

The clinical threshold is 4. Studies in sarcoidosis typically report mean scores of around 4.5 to 5.5 in fatigued patients. So 7.0 is at the far end even of that range.

Here’s the thing about the FSS though: it was built to detect fatigue, not to track it in someone who is already at maximum. It will say 7.0 every time. It’s been 7.0, in effect, for eight years. As a tracking tool it’s useless. As a single clinical statement — maximum score, consistent for eight years — it’s actually quite powerful. It’s unambiguous in a way that a description rarely is.

So if you’re thinking about measuring your own fatigue, the choice of scale depends on what you’re trying to do. If you want something to show a doctor, FSS is quick and the score is immediately legible to any clinician. If you want to understand the shape of your fatigue — where it hits you, whether it’s more physical or cognitive — MFIS gives you more to work with, if you have the capacity to complete it.

Pick the one you can actually finish on a bad day. That’s the one that will give you real data.