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A diagnosis of multiple sclerosis may be delayed in the presence of other chronic illnesses, new research indicates.

A diagnosis of multiple sclerosis may be delayed in the presence of other chronic illnesses, new research indicates. As a result, these patients are prone to greater disability once the neurologic condition is recognized.

"Our study suggests that doctors who treat people with chronic diseases should not attribute new neurological symptoms, such a numbness and tingling, to existing conditions without careful consideration," lead author Dr. Ruth Ann Marrie said in a press release.

To determine the effect of preexisting comorbidities on the diagnosis of multiple sclerosis (MS), Dr. Marrie, at the University of Manitoba in Winnipeg, Canada, and colleagues in the US surveyed close to 9000 patients enrolled in the North American Research Committee on Multiple Sclerosis (NARCOMS) Registry in 2006. Their study was published online on October 29 by Neurology.

The average interval between symptom onset and diagnosis of MS was 7.03 years. The data show that diagnostic delay decreased steadily over time, from an average of 10.6 years prior to 1981, to 1.12 years in those who developed symptoms after 1999. The delay was also shorter among older persons.

"The mean diagnostic delay was consistently longer in the presence of vascular, autoimmune, musculoskeletal, gastrointestinal, visual, and mental comorbidities," the authors report.

Among patients less than 25 years old when MS symptoms began, a preexisting condition increased the average time to diagnosis by up to ten years. For those between 25 and 40 years of age, the mean difference between those with and without comorbidities ranged from 2.0 to 4.7 years; for older subjects, the difference was 0.6 to 2.3 years.

To examine how comorbidity affects the degree of disability at diagnosis, Dr. Marrie's group studied 2400 persons who enrolled in NARCOMS within two years of diagnosis. Those with any physical comorbidity were more likely to report moderate vs mild disability at diagnosis (adjusted odds ratio 1.66). Each additional comorbidity increased the odds of moderate disability by 13 per cent, and the odds of severe disability by 18 per cent.

The data suggest that the relationship between other illnesses and disability "could be partially mediated by the diagnostic delay," the authors say. On the other hand, they suggest, "comorbidities could act pathophysiologically to increase disease progression."

"Future studies should evaluate the underlying mechanisms of these associations and determine how treatment of persons with MS and comorbidity can be optimized," they conclude.

Neurology 2008