OBJECTIVE: To determine the correlation between single breath count test and neck flexors muscle strength with spirometry.
BACKGROUND: Respiratory muscle weakness leading to hypoventilation and respiratory failure is the most serious complication of myasthenia gravis. Although formal spirometry is the "gold standard" for determining impending respiratory failure, such testing is often impractical, delayed, or unavailable. A simple, accurate bedside test that accurately measures pulmonary function is therefore highly desirable. Anecdotal evidence has suggested that surrogate measures such as single breath count test (SBCT) and neck flexor strength correlate with spirometry and respiratory muscle strength.
DESIGN/METHODS: This was a prospective, cross-sectional, single-blind study done in adult patients (> age 18) with antibody positive myasthenia gravis. SBCT was performed by asking patients to take a deep breath and start counting as far as possible in their normal voice with the approximate rate of 2 counts per second. Neck flexor strength (supine) and shoulder abductors (sitting) were graded using modified MRC. Spirometry was then performed blindly by a trained respiratory therapist.
RESULTS: Twenty-one patients (14 males and 7 females; MGFA grade 1-3) age 20-81 (mean± SD 57 ±19) were studied. SBCT (range 16-40; mean 28 ±7) showed a strong correlation with FVC (p=0.01). There was no relationship between shoulder abductor strength and FVC but neck flexor strength showed significant correlation (p=0.02).
CONCLUSIONS: Our data suggest that SBC and neck flexor strength testing are potentially valuable tools for bed side assessment in MG patients. Further assessment of these bed side tests in a larger group of patients of varying severity is ongoing.
Disclosure: Dr. Elsheikh has received research support from Abbott. Dr. Arnold has nothing to disclose. Dr. Gharibshahi has nothing to disclose. Dr. Reynolds has nothing to disclose. Dr. Freimer has received research support from Alexion Pharmaceuticals. Dr. Kissel has received personal compensation for activities with Alexion Pharmaceuticals and Cytokinetics. Dr. Kissel has received research support from Abbott Pharmaceuticals and the NIH.
note :
The Counting Test
o take a huge breath and count aloud. Determine how high the patient can count in one breath. If the patient can count to "10" on one breath they likely have a forced vital capacity of about 1000 ml, if they can count to "25" then the vital capacity can be estimated at about 2000 ml.
(http://www.lilywhite.us/myasthenia)
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