Subjective memory complaints (SMC)

Memory complaints are common among older adults and often considered an initial symptom of cognitive impairment; possibly heralding the onset of a dementia syndrome (Reisberg et al., 2008). This is evidenced by their inclusion in the criteria that define MCI. Subjective memory complaints (SMC) refers to reports of concern about memory performance in relation to everyday functioning, such as remembering names and recalling where one has placed things in response to a question on memory (Coley et al., 2008; Mitchell, 2008b).

Self-reports of memory loss are generally perceived as problematic and have been criticised on several grounds (Ahmed et al., 2008; Jungwirth et al., 2004). The techniques used to assess SMC vary widely across studies; some use a single question on everyday abilities or probe about changes in memory (Estevez-Gonzalez et al., 2003; Palmer et al., 2003; Kim et al., 2006), whilst others use questionnaires to define SMC (Perri et al., 2007), such as the Memory Assessment Clinic-Questionnaire. The clinical significance of each method remains to be determined, as not all measurement techniques are equal. The lack of consensus on the criteria that define and quantify SMC has produced inconsistent reports regarding its clinical utility (Abdulrab and Heun, 2008; Mitchell, 2008a).

Furthermore, the complaint is not always detected on psychometric testing or spontaneously disclosed when questioned directly (Lavery et al., 2006), despite being consciously aware of a change in their memory (Lam et al., 2005b; Wong et al., 2006). In this regard, subjects with a clinically

significant disorder can be excluded, underestimating the clinical utility of MCI and progression rates to dementia (Mitchell, 2008b). Jungwirth et al.

(2004) reported that a significant number of their subjects with objective memory impairment (94%) did not complain about their memory. This issue is problematic for the concept of MCI and has led to calls for the removal or separation of SMC from MCI (Purser et al., 2006; Mitchell, 2008b).

It has been demonstrated that patients with more severe cognitive impairment or with Alzheimer’s disease underestimate their memory difficulties compared to informant information (Farias et al., 2005). A meta-analysis examining the clinical significance of SMC reported that 60% of people with dementia do not complain of simple memory complaints even on specific questioning (Mitchell, 2008b). It has been suggested that patients in the early to mild stages of Alzheimer’s disease have poor insight into their memory difficulties (Kim et al., 2006). In this regard, recommendations specify this information can be provided by a relative or reliable informant, such as a general practitioner (Mackinnon et al., 2003; Winblad et al., 2004).

However, whilst this is important in severely impaired subjects, the information provided by an informant may introduce bias. Some subjects may be able to hide problems by the use of lists and other strategies. Thus, only those with more severe impairment would be noticed by informants.

It remains unclear, however, whether SMC are a useful clinical indicator. Some studies of elderly subjects have reported an association between SMC and a subsequent diagnosis of dementia (Geerlings et al., 1999; Jorm et al., 2005b; St John and Montgomery, 2002; Wang et al.,

2004a; Wong et al., 2006). Jorm et al. (2005b) reported older males who developed dementia had SMC at least 3 to 6 years earlier, often before objective deficits could be measured on tests of episodic memory, orientation and language. Other studies have not supported the association (Cargin et al., 2008; Jessen et al., 2007; Minett et al., 2008) and have attributed it to older age (Park et al., 2007; Treves et al., 2005). Further discussion of the relationship between memory complaints and objective memory impairment and dementia is provided in section 3.6.

Subjective memory complaints are common across a range of clinical disorders, and are consistently reported to be associated with psychoaffective disorders, such as depression, anxiety (Jorm et al., 2001;

Jungwirth et al., 2004; Lautenschlager et al., 2005; Minett et al., 2005;

Minett et al., 2008; Wong et al., 2006), personality disorders and neuroticism (Dux et al., 2008). A report by Lautenschlager et al. (2005) showed that SMC are more prevalent in subjects with depression and anxiety than with dementia. Psychoaffective factors could lead to an overestimation of memory problems, especially in those with MCI (Kumar et al., 2006). It is well known that subjects with depression overestimate their memory difficulties and complain more spontaneously (Steffens and Potter, 2008).

However, not all studies support the link between depression and SMC (St.

John and Montgomery, 2002).

The connection between memory complaints and Alzheimer’s disease is rather complex and many factors have been implicated in the relationship.

Some of these include; older age, psychological factors and different

measurement and techniques. This makes the cognitive burden incurred by patients presenting with SMC difficult to objectively measure, especially in the early stages of disease when memory complaints are difficult to assess.

All of these factors have made it difficult for SMC to consistently predict dementia.

Nevertheless, SMC play an important role in the pathway to care for persons with cognitive disorders. Whilst SMC may be non-specific to a number of disorders and their role in diagnostic criteria may require further refinement, they do seem to increase the likelihood that the individual will seek medical attention. Thus, identifying a cohort that may better respond to the available treatment therapies.

Collectively, these issues have led to uncertainty about the clinical significance of SMC, especially in defining MCI. Disagreement remains with respect to the aetiology and clinical significance of SMC. Reports are now calling for memory complaints to be separated from MCI (Allegri et al., 2008;

Mitchell, 2008) and for a consensus to be reached on the criteria to define SMC that reliably predict progression to MCI (Reisberg et al., 2008). The separation of SMC from MCI may help to clarify the role of SMC in cognitive function and possibly represent a step towards earlier diagnosis.