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Assessment of cognitive dysfunction is an essential part of determining the severity of a patient’s depression. Monitoring cognition (as well as emotion) from the initial diagnosis of depression ensures that all aspects of the patient’s condition are considered, and increases the chance of preventing future relapse and improving treatment outcomes.1
Assessments of cognitive function2
Cognitive symptoms of depression can be assessed by a number of subjective scales, questionnaires and scores, and by a variety of objective neuropsychological assessments.3 These can either be administered by the healthcare practitioner (clinician-rated scales), or completed by the patients themselves (patient-rated scales), as below:
Objective neuropsychological tests of cognitive function
Digit symbol substitution test (DSST)
The DSST is an assessment of executive function, and was formed as an original component of the Wechsler Adult Intelligence Scale.4,5 Usually administered manually, the subject is provided with a sheet containing a digit: symbol code whereby each of nine numbers is matched with a different symbol. On the same sheet, a series of digits from the code are presented in a random order. The subject must then draw the symbol that correctly corresponds to each digit, attempting to correctly match all nine to their corresponding symbols in a 90 second period.5 The number of correctly matched digit: symbol combinations is used to indicate performance, with more correct matches correlating with greater cognitive performance.5
Rey auditory verbal learning test (RAVLT)
The RAVLT is an assessment of verbal learning and memory, in which a physician reads a series of fifteen words, and the subject must repeat as many as they can remember, in any order. This is then repeated five times, using the same series each time.6 A second series of words is then read aloud, and the subject is given one chance to recall as many words as possible from this list. Following this, the subject is then asked to recall as many words as possible from the first list. The subject can achieve a maximum possible score of 75, gaining one point for every word successfully recalled from the first series, with higher scores indicating greater cognitive performance. A separate maximum score of 15 can be achieved from the delayed recall aspect of this test, whereby the subject achieves one point for each word they can remember from the first series, following completion of the second set of words.The delay in this assessment will depend on the time taken for the patient to complete five rounds of recall from the first series of words, coupled with the time taken to recall as much of the second series as possible. Higher total scores indicate greater cognitive functioning.7
Choice reaction time test (CRT)
A digitally-administered test of attention, the CRT test requires the subject to select either the right or left button on a pressure pad, depending on which side of the screen a stimulus appears following a random delay.8 This is repeated 80 times, and scoring is determined by the mean reaction time, with greater scores indicating more severe attention deficit.9
A digitally-administered test of working memory, the N-back test requires users to recognise when a stimulus appears on a screen and record its location using the arrow buttons on a keyboard. 25 of these trials constitutes one series. The subject then repeats this test, but now records the location of the stimulus one step behind the sequence of stimulus locations displayed on screen – this is the 1-back test. This continues up to three steps behind that displayed, gradually increasing working memory load with each step.10 Subjects produce final scores for both accuracy and reaction time, with lower accuracy and greater reaction times indicating more severe impairment of working memory.10
Simple reaction time test (SRT)
This is a digital test of psychomotor speed, and requires users to click as soon as they see a stimulus appear on a screen following a random delay. This test comprises two series of 50 trials each, with a short break between the series to give the subject a brief rest. Upon completion of the assessment, the subject’s mean reaction time can be calculated, with greater time indicating more severe impairment.11
This is an assessment of executive function and cognitive flexibility. Subjects are required to read as many words as possible off a card within a 45 second period. They then must do the same with a second card on which a number of X’s are written, and name the colour of the ink in which each X is written. Finally, a third test requires subjects to read a card on which a number of colours are written, but to name the ink colour of each word, rather than the written colour itself.10 Scores are determined by the number of items completed correctly within the time limit for each test, with lower scores indicating greater deficit in executive function.2
Patient-rated assessments of cognitive function
The tests described below are some of the more commonly used patient-rated scales in the assessment of cognitive performance in depression. However, this is by no means a definitive list of all available
patient-rated assessments, and others are also used.
Perceived Deficits Questionnaire (PDQ)
The PDQ is a 20-item, patient-reported assessment of cognitive impairment which was originally used as part of a larger battery of health-related quality of life assessments to monitor depression in multiple sclerosis patients.12 The items each assess areas of cognitive difficulty experienced by patients with depression, including difficulties with organisation, memory, focus, planning and processing speed. Each item is scored on a scale of 0 (never) to 5 (almost always), depending on how much each statement relates to the patient’s own experiences.12 The maximum possible score on the PDQ is 100, with higher scores indicating more severe cognitive dysfunction.
The Massachusetts General Hospital Cognitive and Physical Functioning Questionnaire (CPFQ)
The CPFQ is a patient-reported assessment of cognitive dysfunction (and daily functioning) in mood and anxiety disorders including depression. It assesses the seven most common aspects of cognition which can be impaired according to complaints from patients, including alertness, motivation, attention, memory, lethargy, lexical access and mental acuity.13 Each domain is assessed on a patient-rated scale from 1 (greater than normal) to 6 (totally absent), providing a maximum total score of 4213 with scoring brackets as below:14
- ≤7: Greater than normal functioning
- 8–14: Normal functioning
- 15–21: Minimally diminished functioning
- 22–28: Moderately diminished functioning
- 29–35: Markedly diminished functioning
- 36–42: Totally absent functioning
References
- Greer TL et al. Defining and measuring functional recovery from depression. CNS Drugs 2010; 24(4): 267-284.
- Culpepper L. Cognition in MDD: Implications for primary care. In: Cognitive dysfunction in major depressive disorder. Ed: McIntyre R, Cha D, 2015.
- Cusin C, Yang H, Yeung A, Fava M. Rating Scales for Depression. In: Handbook of Clinical Rating Scales and Assessment in Psychiatry and Mental Health. Current Clinical Psychiatry 2010; 7-35.
- Wechsler D. The measurement and appraisal of adult intelligence. 1958.
- McLeod DR et al. An automated version of the digit symbol substitution test (DSST). Behaviour Research Methods and Instrumentation 1982; 14(5): 463-466.
- Schmidt M. Rey auditory verbal learning test: a handbook. Los Angeles Western Psychological Services 1996.
- Barzotti T et al. Correlation between cognitive impairment and the Rey auditory-verbal learning test in a population with Alzheimer’s disease. Arch Gerontol Geriatr Suppl 2004; 9: 57-62.
- Choice Reaction Time (CRT). Available at:http://www.cambridgecognition.com/tests/choice-reaction-time-crt. Accessed July 2015.
- Choice Reaction Time. Available at:http://www.cogtest.com/tests/cognitive_int/crt.html. Accessed July 2015.
- Miller KM et al. Is the N-Back task a valid neuropsychological measure for assessing working memory? Arch Clin Neuropsych 2009; 24: 711-717.
- Simple Reaction Time Test. Available at: http://www.cogtest.com/tests/cognitive_int/srt.html. Accessed July 2015.
- Lovera J et al. Correlations of Perceived Deficits Questionnaire of Multiple Sclerosis Quality of Life Inventory with Beck Depression Inventory and neuropsychological tests. J Rehabil Res Dev 2006; 43(1): 73-82.
- Fava M et al. Reliability and validity of the Massachusetts General Hospital Cognitive and Physical Functioning Questionnaire. Psychother Psychosom 2009; 78: 91-97.
- Roffman JL et al. Chapter 6: Diagnostic rating scales and psychiatric instruments. In: Massachusetts General Hospital Comprehensive Clinical Psychiatry. Ed: Stern TA, Fava M, Wilens TE, Rosenbaum JF, 2008.
