A recently published study finds that the Inclusion Body Myositis Functional Rating Scale (IBMFRS) does not correlate as well as expected with measures of grip strength and finger flexor strength. This suggests that the IBMFRS could be improved to more accurately evaluate the progression of disease. Additional findings are that poor grip strength does distinguish IBM patients from healthy control patients, and that duration of symptoms does not accurately predict the severity of this variable disease.
Inclusion body myositis causes progressive muscle weakness and has a tendency to especially affect the muscles that flex the fingers. In fact, the deep finger flexors are the muscle group most consistently affected at that time of diagnosis.
The IBMFRS is a 10-item questionnaire that evaluates a person’s ability to perform various activities of daily living, such as climbing stairs, turning in bed, swallowing, and dressing. It is used to measure the severity of disease and to monitor how the disease progresses over time. It has been used to evaluate the success of drugs in clinical trials for IBM.
Three of the 10 questions on the IBMFRS are about hand function:
- Cutting food and handling utensils
- Fine motor tasks (opening doors, using keys, picking up small objects)
Participants in the study answered the 10 questions on the IBMFRS and had their grip strength and finger flexor strength measured. The study included 81 IBM patients and 74 healthy control patients who did not have myositis or arthritis.
The results of the IBMFRS were compared with grip strength and finger flexor strength using Pearson correlation analysis, which results in a number between -1 and +1. If the result is between 0 and +1 it indicates that the two items being compared move together in the same direction; for example, the IBMFRS score decreases as grip strength decreases. A result of +1 would mean that the two items move perfectly together, but a low number, like +0.1, would mean that there is very little correlation and the result is almost random.
Taken together as a group, the 3 questions on the IBMFRS had a correlation number of 0.49 when compared to grip strength and 0.45 when compared with finger flexor weakness. This indicates that there is only a moderate correlation. Of the three questions, cutting food and using utensils was most strongly correlated with the strength measures, and handwriting was least correlated.
Finger flexor weakness had to be severely decreased before it had a significant effect on hand function, as measured by the IBMFRS.
This study concludes that the IBMFRS could be improved by finding questions that are more sensitive in detecting changes in IBM patients with mild to moderate muscle weakness.
Data was collected from patients at the 2018 Annual Patient Conference of The Myositis Association in Louisville, KY.
The author of this blog article, Kevin Dooley, MD, assisted in study design and data collection, and is a co-author of the journal article.
Ava Yun Lin MD, PhD , Maggie Clapp , Elizabeth Karanja , Kevin Dooley MD , Conrad C. Weihl MD, PhD , Leo H. Wang MD, PhD , A cross-sectional study of hand function in inclusion body myositis – implications for functional rating scale, Neuromuscular Disorders (2019), doi: https://doi.org/10.1016/j.nmd.2019.12.002
The study was partially funded by the Cure IBM Research Fund at Washington University, St. Louis. Donations to this fund can be made here.