Quantitative assessment of motor fatigue in amyotrophic lateral sclerosis.

Motor fatigue is a common complaint in patients with amyotrophic lateral sclerosis (ALS), but is often excluded, unlike weakness, from the clinical assessment of these patients. This could be due to the complexity and often painful assessment techniques of this motor deficit. This study examines the feasibility of quantitative assessment of motor fatigue by modifying presently available force measurements. The relationship between weakness and fatigue in ALS patients was also examined. Fifty-four ALS patients and 39 normal control subjects performed 30 s of sustained maximal voluntary isometric contraction (MVIC) of elbow flexors (EF), knee extensors (NE), and ankle dorsiflexors (DF), using a computerized force measurement system and standardized testing procedures. Fatigue index (FI) was digitally calculated, from the force-time curve, as the percentage of MVIC unable to be sustained over the 30-s period. Fatigue was greater in ALS patients than in normal control (mean=23% vs. 15%) in all muscles including muscles that were not clearly weak. Weakness and fatigue were poorly correlated in ALS patients and may be independent measures of the pathogeneses of ALS.

Functional magnetic resonance imaging (fMRI) clinical studies in ALS--paradigms, problems and promises.

Functional magnetic resonance imaging (fMRI) provides high-resolution, non-invasive estimates of neural activity detected by a blood oxygen level dependent signal by assessing the increase in blood flow to the local vasculature that accompanies neural activity in the brain. fMRI studies with standard hand motor test (index-thumb opposition, ITO, or pinch) in ALS patients show good test-retest reliability and similar amplitude of signals in ALS patients compared with control subjects. Isometric force can be performed with careful control for the force exerted, recruitment of other muscles and motion artefact. The volume (number of voxels above threshold) of sensorimotor and cerebellar cortex activated by ITO is reproducibly larger in ALS patients compared with control subjects. Imagined movements in ALS have been studied, as in amputees, and larger volumes are activated in ALS patients with imagined movements as well, compared with control subjects. fMRI studies in ALS patients evaluating cortical activation during pure somatosensory stimulation cutaneous stimulation of the hand to elicit the palmomental response and cutaneous stimulation of the sole to elicit the plantar response - indicate that ALS patients activate a significantly smaller volume of the contralateral sensorimotor cortex compared to control subjects. No statistically significant difference was seen in other areas, including the ipsilateral cerebellum and the contralateral thalamus. An anterior shift in the volume of cortex activated by these paradigms occurs in ALS patients, with a volume of activation, anteriorly, not activated in control subjects. fMRI studies will complement other clinical neurophysiological and neuroimaging techniques in our future attempts to solve the riddle of ALS and other motor neuron diseases.