The dreaded global burden of dementia, its extensive research and the possible available tools of prevention have led to the need to be able to differentiate early between normal and pathological aging. Therefore, the concept of mild cognitive impairment (MCI) has been introduced in recent decades. The history of mild cognitive impairment has gone through many stages throughout until it has reached its nowadays accepted, but ever-changing state. As early as 1962, the concept of Benign and Malignant Senescent Forgetfulness was used [1]. In 1986, the National Institute of Mental Health (NIMH) proposed Age-Associated Memory Impairment to distinguish more easily between the two [2]. From 1982, the predecessor of MCI, the mild cognitive decline, was used to correspond to grade 3 on the Global Deterioration Scale, and from 1988 onwards as MCI [3]. In 1994, the concept of Age-Associated Cognitive Decline was introduced, with dementia being the exclusion criterion [4]. The concept of Cognitive Impairment No Dementia was introduced in 1997 and included a larger patient population because the underlying cause was irrelevant and could include mental decline in psychiatric or somatic and neurological diseases [5]. And beyond that, the conceptualists came up with more ideas.
Diagnostic criteria
In 2003, an international committee (Key Symposium) was held to discuss and consolidate the knowledge gained so far, establishing criteria, organizing the knowledge available, and formulating guidelines for disease assessment regarding the involvement of neuroimaging, biomarkers and genetics [6-8]. According to this committee, the MCI criteria are shown in Table 1.
Once diagnosed as MCI, the path of the subtypes can be divided in two ways: if memory is impaired, it is the amnestic type, or, if not, the non-amnestic type. Within each, we distinguish single or multiple domain involvement [7].
In 2011, the National Institute on Aging (NIA) and the Alzheimer's Association (AA) established specific criteria for MCI due to Alzheimer's and later to Parkinson's disease [9]. The diagnostic categorization of the Mayo Clinic's Alzheimer's Disease Research Center places the disease (MCI) between normal aging and dementia. Their diagnostic criteria are as follows: 1, memory complaint, preferably confirmed by an informant; 2, objective memory impairment for age and education; 3, preserved general cognitive function; 4, intact activities of daily living; and 5, not demented [10]. Earlier diagnostic manuals [e.g. Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR)] have been used to encode this heterogeneous group of diseases with different coding. According to the current Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5), it can be categorized as Mild Neurocognitive Disorder [11]. See Table 2. for the diagnostic criteria.
Epidemiology
The results of epidemiological studies have led to significant differences due to the immaturity of the concepts and the different formulations of criteria. To overcome these difficulties, a 2015 cohort study combined the criteria and found that the prevalence of MCI among those over 60 was 5.9% [12]. A Mayo Clinic study published in 2012 found that the incidence of MCI in the 70-89 population was 63.6/1000 person-years [13] A smaller follow-up study found that the conversion rate for community-selected participants was 5% person-years [14]. We found no data about the incidence or prevalence of the Hungarian MCI or AD population, the number of the patients available is based on the estimated number of patients of the international literature.
Assessment
The most commonly used procedures in Hungary for the identification of the disease are the Mini-Mental State Exam or the Early Mental Test developed by the University of Szeged [15]. There is no international consensus on which is the best test and with which cut-off points. In recent years, the Montreal Cognitive Assessment and the Short Test of Mental Status have been used for this purpose, the Hungarian version of which is not yet available [16]. In the field of biomarkers, amyloid deposits or neuronal degeneration are being investigated, which we have not been able to do in routine clinical practice, as well as genetic testing, for which there is no accepted gold standard yet.
We have selected a short, self-completed test method developed by the English author Jeremy Brown, which is validated in different countries worldwide, also in Hungary (TYM-HUN) [17, 18]. This is the Test Your Memory (TYM), which examines a fairly wide range of cognitive functions in a short period of time and provides reliable information to the clinician when properly evaluated [19]. Our study aimed to compare the diagnostic utility of the TYM-HUN with the MMSE and the ADAS-Cog tests for MCI in a Hungarian population. We determined a 'cut-off' point of TYM-HUN where optimal sensitivity and specificity values were obtained to screen MCI.