NASHVILLE, Tenn. – Recent research into comorbidities in multiple sclerosis – including head-scratching findings about lower cancer rates – is shedding light on the links between the disease and other illnesses, according to an epidemiologist specializing in MS.

“People should be mindful that if they look at having a positive impact on those comorbidities, they may have the ability to benefit patients in context of their MS,” Helen Tremlett, PhD, said in a video interview at the annual meeting of the Consortium of Multiple Sclerosis Centers. She is the Canada Research Chair in Neuroepidemiology and Multiple Sclerosis at the University of British Columbia, Vancouver.

In recent years, research into comorbidities in MS has risen dramatically. Dr. Tremlett found that the number of papers per year in PubMed that address MS and comorbidity has risen from roughly 30 in 2007 to about 80 in 2015, although the numbers dipped to about 50 and 60, respectively, in 2016 and 2017.

A 2015 systematic review of research into MS and comorbidities reported that while “findings were inconsistent overall,” studies suggested that “meningiomas and possibly urinary system cancers, inflammatory bowel disease, irritable bowel syndrome, epilepsy, depression, anxiety, bipolar disorder, early cataracts, and restless legs syndrome were more common than expected in the MS population.” (Mult Scler. 2015 Mar;21[3]:263-81).

Notably, most cancers are missing from this list. In fact, Dr. Tremlett cowrote a 2012 study that found lower risks of all cancers and several specific types of cancer – breast, lung, colorectal, prostate, and melanoma – in MS patients, compared with age- and gender-matched controls (Brain. 2012 Oct;135[Pt 10]:2973-9).

According to Dr. Tremlett, there are several theories about the apparent lower cancer risk in patients with MS. Perhaps their immune systems are hypervigilant, or maybe MS diagnoses inspire healthier lifestyles.

Researchers have been intrigued by another possibility – that cancer diagnoses are being delayed in patients with MS. Indeed, the 2012 study found that tumor sizes at diagnosis in patients with MS were larger than expected in breast, prostate, lung, and colorectal cancer (P = .04).

“We couldn’t record why that’s the case, but there may be some so-called ‘diagnostic neglect,’ ” she said. “You could imagine a scenario where a typical person with MS goes to see their physician and says, ‘I’m tired. I have fatigue,’ and the physician says, ‘Yes, you have MS, that’s what you should expect.’ Someone in the general population might get additional investigation, get blood work done, and their cancer might be found earlier.”

It’s also possible, she said, that cancer isn’t picked up earlier because it can be difficult to screen people with disabilities. “It’s only recently that physicians can offer the Pap smear to women in a wheelchair.”

On another front, there’s evidence linking comorbidities to worsening MS. A 2018 study coauthored by Dr. Tremlett found that patients with more comorbidities had more disability. Specifically, ischemic heart disease and epilepsy were associated with greater Expanded Disability Status Scale scores (Neurology. 2018 Jan 3. doi: 10.1212/WNL.0000000000004885).

Other research coauthored by Dr. Tremlett has linked comorbidities in MS – specifically, hyperlipidemia, migraine, and three or more comorbidities – to higher risk of MS relapse (Neurology. 2017 Dec 12;89[24]:2455-61).

Dr. Tremlett reported having no relevant disclosures.

Inside the complex, surprising world of MS comorbidities