Home > meeting report > Meeting report (part 4b): evaluating muscle function in inflammatory myopathies

Meeting report (part 4b): evaluating muscle function in inflammatory myopathies

Advances in basic experimental as well as clinical research on pathophysiological mechanisms and treatment opportunities of various rheumatoid disease conditions have been complicated or frustrated by issues like how to define a disease (i.e. proper diagnosis) and how to define measurement of treatment response (i.e. which outcome measuers should be targeted and evaluated in trials). In this blog, after putting things in a broader context shortly, I will write what I learned about evaluating disease activity of inflammatory myopathies in daily clinical practise, and to be more precise evaluating muscle functioning. Two standardised examinations are available for that purpose: the MMT-8 and the FI-2.

What do we measure at all without proper definitions of disease and disease activity? (the context)
(When you think you know the context you might just skip this section and start redaing about measuring disease activity in inflammatory myopathies)
Ideally all investigators of course want a study population that is as homogenous as possible to get a maximum answer on the question: when I do this or that in disease X, does that help or not for this specific disease condition X? Based on our steadily growing insights on underlying pathophysiological mechanisms of several rtheumatic diseases (thanks to a lot of work performed in laboratories in basic research) the definition or classification of rheumatic diseases is adjusted and “narrowed” to specific pathophysiologic mechanisms in order to diminish heterogenity of study populations. But even when you have created a fairly homogeneous study population, differences may still exist in terms of disease duration or stadium, proportion of reversible (nflammation) or irreversible (tissue damage) characteristics, etctera. A number of these can of course be ruled out by applying strict inclusion criteria (e.g. maximum disease duration, or age).
Now that study populations are more and more well-defined and homogenity is maximised, an other challenge remains. A challenge that is equally important as defining a specific disease is how to define whteher that specific disease is active or not and whether this activity is succesfully influenced by the treatment intervention. Defining disease activity is however easier said then done. Whereas some rheumatic conditions provide clinical and laboratory clues on inflammation as a sign of disease activity, and some diseases clinically “flare” every now and then (e.g. rheumatoid arthritis, lupus) others may clinically and based on lab results show a rather stable slowly progressive course of disease (e.g. Sjögren’s sydnrome) in which only loss of function or tissue damage can be quantified. For inflammatory myopathies it is somewhere in between in this spectrum of detectable (or not) disease activity phenomenons. Clinical signs and symptoms, next to e.g. changing values of muscle enzymes on bloodwithdrawals do give an indication of disease activity in inflammatory myopathies, however in daily clinical practice things can be much harder to define and detect then one would think absed on the etxtbook knowledge just mentioned. Changes in disease activity can be rather subtile, or can e.g. not always be accompied by elevated muscle enzymes. Also having a bit of disease activity or having no disease activity of inflammatory myopathy can really make a difference and have a significant impact for the patient in daily lfie. So it is important to asses and monitor disease acrtivity in a very secure and precise way to adjust, if necessary, the treatment given to the patient, and to prevent unnecessary loss of muscle tissue (damage) plus accompanying loss of function and quality of life for the individual patient. It is very much the same way of thinking about controlling inflammatory myopathies as like (tight) controlling arthritis.

How to monitor disease activity in inflammatory myopathies?
Next to monitoring ESR, CRP or CPK levels on routine blood examinations, and of course what the patient reports regarding experienced disease activity (e.g. measured using the HAQ and VAS scales), the performance of the muscles can be examined in a standardised manner in order to quantify muscle functioning. In inflammatory myoptahies currently two ways of doing so are recommended, and also used in the study design of recently pubished manuscripts. One is the Manual Muscle Test (MMT)-8. Together with extramuscular assessment tools like the Myositis Disease Activity Assesment Tool (MDAAT) or Myositis Intention to Treat Activity Index (MITAX), and the HAQ, VAS and serum activity of 2 or more muscle enzymes (CK, LD, AST, ALT, aldolase) they form the components of the Idiopathic Inflammatory Myopathy Disease Activity Core Set (click for full description and downloads) that has been put forwrad by the International Myositis Assessment & Clinical Studies Group (IMACS) of outcome parameters. Next to using the MMT-8 the other test for muscle functioning is the so-called Functional Index of Myositis, the revised version is named FI-2 [1]. The FI-2 is, according to Professor Lundberg from the Karolinska Institute at Stockholm, Sweden, more sensitive then the MMT-8 but also more time-consuming to perform in daily clinical practice.

The Manual Muscle Test -8 (MMT-8)
The MMT-8 is officially decsribed as: “This partially validated tool assesses muscle strength using manual muscle testing (MMT). A 0 – 10 point scale is proposed for use. An abbreviated group of 8 proximal, distal, and axial muscles performs similiarly to a total of 24 muscle groups, and is also proposed for use for research studies.”

The 8 muscle groups included are the deltoid, biceps and wrist extensors in the upper extremity, the quadriceps, gluteus maximus, gluteus medius and ankle dorsoflexors of the lower extremity as well as the neck flexors. They are tested unilaterally, generally on the right side (thus, the maximum MMT-8 score is 80). The MMT-8 is a shortend and more practical version of the MMT-24 test in which, as the name suggests, more muscle groups are tested bilaterally.

The mentioned weblink offers several educational materials amongst with PDF documents that give an extensive explanation of the MMT-8, like this one (PDF). There is also eductional video material on that website, but unfortunately the videos do not play in my browser.

The revised Functional Index of Myositis: FI-2
The functional index of myositis was actually developed by the Karolinska Institute in Sweden and tries to combine testing for both muscle strength and endurance. This is done by counting the number of repetitive standardised movements of 7 muscle groups. [1]

The rationale for developing this FI-2, according to the authors:
“The MMT and kinetic systems or Cybex devices have been used in trials to assess isometric muscle strength in myositis. However, the MMT could have limited measuring reliability in patients with mild impairment. Isokinetic measurements were used in one trial including patients diagnosed with inclusion body myositis (IBM), but have not yet been used in patients with polymyositis (PM) and dermatomyositis (DM). These systems are costly and not feasible in daily clinical practice. Another limitation of these measurements is that they measure strength, although patients with PM and DM often report impaired muscle endurance in addition to muscle weakness.”

How the FI-2 should be performed is described in this PDF document.

From that PDF document on FI-2 testing:
**Instruction to patient:
– Perform as many repetitions of each task as you can, or stop when reaching maximal number of repetitions. However, you decide when to stop due to muscle fatigue, pain or general fatigue.

**Instruction to observer:
– Numbers of correct performed repetitions following five learning repetitions are registered for each task.
– If passive ROM is normal, but active ROM is limited the score is 0. Do not perform the task. If passive ROM equals active ROM perform the task within actual ROM.
– Each task is stopped if: a) the patient can not keep up the given pace and is unable to correct within three repetitions, b) the patient starts to compensate and is unable to correct within three repetitions. After completing each task, the patient is instructed to rate perceived muscular exertion on the Borg CR-10 scale from 0-10 (0=no exertion, 10=maximal exertion).
– A metronome is used to standardize the movement pace of each task.

The patient has to perform 7 tasks with a standardised pace and maximum of repetitions. These are shoulder flexion, shoulder abduction, head lift, hip flexion, a step test, heel lift test and a toe lift test. In the revised version, like in the MMT-8 testing is done unilaterally, generally at the right side.

In the paper I refer to, the authors conclude that “The FI-2 is a valid and reliable outcome measure of impairment for patients with polymyositis or dermatomyositis. It is well tolerated and the unilateral FI-2 requires a maximum of 20 minutes to perform.”
So, there you have an idea of what it involves to perform FI-2 testing in daily clinical practice. Given the more time-consuming character of FI-2 measurements, when implemented in clinical practice there seems a role for nurses or paramedics (physiotherapists being the most logical group with their special expertise on muscle testing). During my trainee posts I was sometimes suggested (by my supervisors) to ask a physiotherapist to perform specific muscle testing in (often clinical) patients, either for diagnostic reasons or for treatment evaluation. I have to admit that, whilst writing this, I (as a rheumatologist) should be using the specific expertise of physiotherapists for assessment of muscle functioning more often.

But I imagine performing quite a “work-out” by completing all the 7 tasks with repeated paced movements as decsribed in the FI-2, could actually be quite a lot of fun to do and to watch 😉

Off topic: In a more general way there is currently much debate in my country where the Dutch government decided to further breakdown the number of physiotherapy treatments that is paid for by the insurance companies and that patients should pay more sessions from their own money, which they do not always have, especially in lower social classes. It is, as a policy, in marked contrast with increasing scientific data that physiotherapy is of real benefit for the course of chronic rheumatic diseases, and that people perform much less daily activity then they are saying to do in questionnaires or surveys. In my opinion in the end the health system and costs would be better of by subsidising and stimulating physiotherapy in some manner instead of breaking it down, with all longterm consequences of worsening diseases and as a consequence increased health care costs on a longterm basis, but who am I, I am not the PM of the Netherlands 😉

To conclude, thanks for reading my blog post, and being curious I would appreciate if you could leave a comment regarding whether you consider to implement either MMT-8 or FI-2 testing in your own rheumatology clinic, why or why not. Let me know, and let’s share some opinions from the field.

Further reading:
**Functional Index-2: full text paper on validity and reliability and mentioned PDF file with instructions.
**MMT-8: and plenty of educational material on the Core Set of Disease Activity measurements in inflammatory myopathies can be found on this website.

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