Age, Comorbidity, Frailty in Observational and Analytic Studies of Neurological Diseases.

BACKGROUND Comorbidities are rarely taken into account in studies of neurological conditions although they may be a confounder of the outcome and treatment. The relationship between comorbidities and neurological conditions is also problematic as comorbidities may be symptoms of the underlying cause of the neurologic condition or long-term adverse effects of the treatment. SUMMARY There is evidence that several common neurological conditions have an increased burden of somatic and psychiatric comorbidities compared with matched samples from the general population. Depression is probably the most common comorbidity. Both psychiatric and somatic comorbidities have been shown to account for some of the premature mortality encountered in these neurological conditions. Comorbidities and age can also be important factors in the response and tolerance to treatment, and can alter the general outcome of a disease. KEY MESSAGES Age and comorbidities should not be overlooked in the observation and assessment of neurological conditions and their treatment.