A study in Europe concluded that Provigil could improve sleep quality and daytime fatigue in mulitple sclerosis patients, and that a lower dose was needed than for people with narcolepsy. Another study seemed to contradict that finding, and showed no benefit to MS patients.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12195441

There are currently clinical trials in process in which researchers are attempting to quantify the effects of provigil in people with muliple sclerosis.

http://clinicaltrials.gov/ct/show/NCT00142402;jsessionid=597415709832174718823DAEF0222D61?order=24

Experts debate the definition and pathophysiology of fatigue in multiple sclerosis and there is no real way to quantify fatigue, which is subjective. But everyone agrees it is an important topic for MS patients. Fatigue is the most frequently reported symptom of multiple sclerosis; it limits activity and participation in many areas of life and causes psychological distress.

Fatigue management is based on a comprehensive evaluation of its characteristics and consequences (sometimes with the use of scales such as the Fatigue Severity Scale and the Modified Fatigue Impact Scale), and on the identification of many potential contributing factors (psychological disorders, sleep disturbances, pain, infections and other comorbidities, medications, and deconditioning). Rehabilitative interventions are essential to the treatment of fatigue. Beyond the traditional energy conservation strategies and cooling techniques, several randomized controlled studies have demonstrated the positive impact of aerobic exercise.

Further, multiple sclerosis patients often experience cognitive impairment, which may share a common physiopathological substrate with fatigue. Not much is known about effective strategies for managing cognitive impairment in multiple sclerosis. Small trials with amantadine, pemoline, 4-aminopyridine and 3–4 aminopyridine have provided mainly negative results.

Update: A Spanish study found Provigil helped multiple sclerosis patients' fatigue and was feasible for regular use.

A Dutch study on modafinil as a possible way to increase activity in people with myontonic dystrophy found that find a significant improvement from the drug.

The National Multiple Sclerosis Society on modafinil

Modafinil for the treatment of multiple sclerosis-related fatigue.

Modafinil for multiple sclerosis fatigue: does it work?