**7. Prognosis of mild cognitive impairment**

Mitchell and Shiri-Feshki analyzed 41 high-quality cohort studies. They have found that the annual conversion rate (ACR) from MCI to dementia is approximately 5–10% and most people with MCI will not progress to dementia even after 10 years of follow-up [39]. The cumulative risk over 10 years ranged between 30 and 50%, depending on whether the studies that were analyzed used a definition of MCI that included subjective memory complaints. Other meta-analyses of long-term (5–10 years) studies reported lower annual conversion rates of 3.3–4.2% and cumulative conversion rate ~31% over 10 years. In fact, a substantial percentage of individuals with MCI actually revert to normal. Sujuan et al. found that the annual reversion rate from MCI to normal cognition was substantially higher (18.6%) than the annual progression rate from MCI to dementia (5.6%) in a study spanning between 1992 and 2009 [44].

Studies suggest that common factors related to MCI reversion include genetics (i.e., fewer APOE ε4 alleles), preserved global functioning, subtype of MCI (i.e., non-amnestic single domain), cognitive functioning (i.e., higher standard scores on cognitive assessments), and neuroimaging (i.e., larger hippocampal volumes) [45]. Huey et al. found that single-domain executive MCI has a better outcome than amnestic MCI and that executive dysfunction in multiple-domain MCI does not independently increase the risk of progression to dementia [46].

It has been shown that as many as 30% of people with MCI have potentially treatable causes of cognitive decline. The most common of these include hypothyroidism, vitamin B12 deficiency, vascular disease, normal pressure hydrocephalus, and subdural hematoma. Another study concluded that changing the risk factors for stroke and treating depression may have contributed MCI reversion to normal [47].

Nevertheless, the proportion of patients with MCI who convert to dementia still remains significant and it is important to identify factors that facilitate progression for adequate prevention and application of both pharmacological and non-pharmacological therapies. Adequate and on timely identification of MCI in definite cases can help to plan effective strategies for prevention of progressive cognitive decline.
