They really don't know much about how the disease-modifying treatments for MS affect older people but they're finding out that aging may make people more susceptible to the infections--like PML--that are sometimes associated with these treatments.
From PubMed, July 3, 2017:
Curr Neurol Neurosci Rep. 2017 Aug;17(:61.
Immunosenescence: the Role of Aging in the Predisposition to Neuro-Infectious Complications Arising from the Treatment of Multiple Sclerosis
Grebenciucova E1, Berger JR2.
Author information
1
Multiple Sclerosis Division, The Department of Neurology, Perelman School of Medicine, The University of Pennsylvania, 3400 Convention Avenue, Philadelphia, PA, 19104, USA. MsNmoSarcoidosis@gmail.com.
2
Multiple Sclerosis Division, The Department of Neurology, Perelman School of Medicine, The University of Pennsylvania, 3400 Convention Avenue, Philadelphia, PA, 19104, USA.
PURPOSE OF REVIEW:
This review highlights some of the important changes in the immune system that occur in the process of normal aging. Immunosenescence as a concept is directly relevant to the world of neuro-inflammation, as it may be a contributing factor to the risks associated with some of the current immunosuppressive and immunomodulatory therapies used in treating multiple sclerosis (MS) and other inflammatory disorders.
RECENT FINDINGS:
Profound qualitative and quantitative changes occur in the adaptive and innate immunity compartments during aging. These changes may explain why patients of older age are at an increased risk of infections and infection-associated mortality. Immunosenescence-associated changes may be additive or synergistic with the effects produced by immunomodulatory and immunosuppressive medications. Clinicians should exercise a high level of vigilance in monitoring the risk of infections in older patients on these treatments.
https://www.ncbi.nlm.nih.gov/pubmed/28669032