Multimorbidity in low- and middle-income countries
Many low- and middle income countries (LMICs) face complex, multiple disease burdens, including chronically-managed infectious diseases and rapidly rising non-communicable diseases [1]. Medical advances, increasing population aging, widespread urbanization and food industry globalization add to this unique epidemiologic transition [2]. About a fifth of adults in LMICs suffer from multimorbidity [3] (defined as the co-occurrence of at least two chronic conditions in an individual [4]) and rates may already surpass those in high-income countries (HICs) [5]. Multimorbidity is becoming an increasing public health concern as it is associated with high levels of disability [3, 6], poor quality of life [7], and raises healthcare costs and -utilization [8] in already financially-constrained public health systems. Additionally, since multimorbidity occurs 10–15 years earlier in LMICs than in less deprived countries [9], these healthcare systems will be strained for longer. Unfortunately, despite recognition of the treatment and rehabilitation challenges associated with addressing multimorbid chronic conditions in a patient, clinical guidelines and health management aspects remain focused on separate singular diseases [10].
Globally, literature on multimorbidity is growing but seems to remain fragmented and poorly understood [4, 5, 11]. Most studies have assessed single diseases or comorbidities in association with an index disease (“comorbidity” is a related yet different clinical entity from “multimorbidity” [4, 12] – see Additional File 1 for a glossary of key terms related to this protocol). Even studies explicitly referring to “multimorbidity” have used different disease count cut-offs, disease combinations, multimorbidity measures and statistical methods for determining patterns; highlighting the current lack of consensus regarding its definition and operationalization [4, 5].
While there is agreement that multimorbidity seem to present in certain disease patterns and leads to functional decline, the available literature is limited, mostly from high-income countries (HICs) and focused among older adults [13]. Such research cannot be generalized to LMICs, where those affected by multimorbidity are relatively younger and the disease patterns are likely different [14].
The lack of agreement on standards for identifying and classifying multimorbidity patterns remains a major challenge in developing clinical guidelines for managing patients with multimorbidity [11]. As the healthcare of people with multimorbidity is unique, complex and different from highly specialized approaches typically tailored to single diseases [4], a better understanding of the occurrence and person-centric impact of multimorbidity patterns would inform the development, planning and delivery of targeted and cost-effective interventions for better patient outcomes.
Multimorbidity and function
There is much evidence to suggest that multimorbidity leads to declines in physical function, and that a higher number, more severe and certain patterns of co-existing conditions is associated with faster functional deterioration [15, 16]. It has been proposed that the interplay between multimorbidity and function may be two-way. Multimorbidity may lead to disease-disease, drug-drug or drug-disease interactions, curtailing compensatory mechanisms and resulting in physical and cognitive deterioration. Poor function, on the other hand, may impact the severity and burden of multimorbidity [15]. Limited available research has for example shown that walking speed and handgrip strength are inversely associated with the development and worsening of multimorbidity, with evidence of a dose–response relationship [17]. As such, a vicious cycle of limitations in self-care and poor patient outcomes may develop [15], which is further exacerbated by a reduced ability to cope with the burden of multiple treatment regimens, increased risk of functional dependence and reduced chances of survival [15].
Establishing relationships between multimorbidity and function has clinical value, especially in primary care, as it has been suggested that simple, low-cost assessments such as walking speed or handgrip strength may be valid markers for clinical evaluation and monitoring, and to use for prevention or intervention, in chronic disease and multimorbidity [17–20].
Multimorbidity patterns
Certain chronic conditions seem more likely to co-exist in associative patterns, possibly due to shared pathophysiological mechanisms or risk factors [21]. It is suggested that some multimorbid disease combinations have larger synergistic effects on health outcomes (including function and disability) and service utilization than others [4, 21, 22]. Multimorbidity has most often been described using simple or weighted disease counts [14]. Although count-based approaches are useful for identifying patients who require complex care [23], they are less helpful for informing clinical guidelines, as no distinction can be made between individuals with a similar amount, but different types, of diseases [11]. Statistical techniques are therefore increasingly used to categorize multimorbidity patterns into distinct non-random or associative classes. Although multimorbidity patterns vary depending on the analytical method used [24], systematic reviews on statistically-determined profiles have described patterns of cardio-metabolic, mental health, and musculoskeletal problems with relative consistency [11, 21]; and it is suggested that replicable and clinically meaningful multimorbidity patterns do indeed exist [11].
Evidence on multimorbidity patterns in the specific context of LMICs, however, remains scare; including information on patterns that may be associated with functional aspects (activity limitations, impairments of body function/structure and participation restriction). It has been suggested that cardio-respiratory, metabolic and mental health patterns are common regardless of country or income level [12, 21]. Other patterns that have been identified in low-resource settings include HIV and anemia [25], mental-articular [12], respiratory (including tuberculosis) [22], mental-sensory, and visceral-arthritic [22, 26].
Studies investigating multimorbidity and function have mostly focused on relationships in terms of the presence/absence of multimorbidity or disease count, rather than multimorbidity patterns per se [26]. Yet multimorbidity may have a different compound impact on function than the expected summed effect of single conditions. Diseases that co-exist in patterns may interact in complex ways, inhibiting compensatory mechanisms, which may lead to more severe functional problems [22, 27].
The severity of chronic diseases, order of onset, temporal evolution and social factors also add to the burden of multimorbidity on the individual [22]. In HICs, patterns of neuropsychiatric diseases have been shown to lead to the greatest declines in functional ability or instrumented activities of daily living (IADL) over time [28, 29], while cardiovascular profiles were associated only with declines in mobility [28] or activities of daily living (ADL) [29]. In LMIC studies, chronic lung disease and tuberculosis [22] and mental-sensory combinations (psychiatric conditions, cognition-related conditions, vision impairment, and hearing loss) [26] have been associated with the worst functional outcomes (measured using walking speed and handgrip strength). Identifying multimorbidity patterns may provide insights on synergies and effects associated with coexisting conditions and aid recognition of more vulnerable patients that need special consideration when formulating care plans, secondary and tertiary prevention [23]. Therefore, identifying and understanding disease combinations that reliably present as patterns may contribute towards the development of guidelines that target specific profiles, risk factors and consequences [11] and may inform comprehensive service configurations to better address patient needs.
Risk factors
Globally, multimorbidity is more reported among people of older age, male sex and unemployed status; while seemingly less common in those with higher education levels and socioeconomic status [12, 25, 30]. Although on a global level there seems to be agreement regarding common profiles of associated factors for multimorbidity, uncertainty remains regarding risk factors that predict specific multimorbidity patterns (due to a lack of longitudinal evidence) [4].
In addition, although risk and/or protective factors for multimorbidity or poor function have been investigated separately, both health constructs have rarely been considered concurrently. Most studies of the relationship between multimorbidity and function have either been cross-sectional or focused on multimorbidity as a one-directional predictor for functional decline incidence [15].
Data on the shared risk factors for multimorbidity and activity limitations of functional impairments thus remain limited [15], and non-existing in LMICs.
If multimorbidity leads to functional problems and/or vice versa, then the existence or development of one of these states may start a cascade effect, with a resulting escalation of risk for other adverse outcomes such as disability, decreased quality of life, and institutionalization. Furthermore, if these phenomena have shared risk factors, then individuals with these characteristics would be at particularly high risk of developing a vicious cycle [15], and this group would be important to target for prevention strategies to mitigate poor outcomes.
Implications for patients and the health system in low- and middle-income countries
Many LMICs continue to battle prevalent infectious diseases in parallel with high rates of non-communicable diseases, and will have to navigate the consequent population health, health systems and economic implications [2, 31]. In South Africa, for example, multimorbid infectious and non-communicable diseases are the commonest in 40 to 60-year‐olds [32]. People of these ages are usually engaged in employment and/or have domestic, family, and social responsibilities. Not only does multimorbidity have potential profoundly negative effects on health and work productivity, but the utilization and cost of care increase exponentially with the number of coexisting chronic conditions in a person [33]. The burden on already resource-constrained health care systems is thus increased [34], even more so if management of associated impairments will be needed at earlier ages and for longer periods.
Unfortunately, most health care systems, including those in LMICs, are structured to provide care in a vertical, disease-specific and curative nature [35, 36], rather than to provide organized care for chronic conditions. This kind of curative approach is often inadequate, inefficient, and ineffective when a multiplex of chronic conditions coexist [37] and unfortunately a high level of unmet treatment needs persists among people with multimorbidity [38].
When healthcare is focused on comprehensive guidelines-based treatment for a single condition (that may have led to a significant event such as hospitalization), concurrent conditions that have a similar or larger impact on the patient’s overall health may be missed [39]. In such scenarios, less (if any) attention may for instance be paid to managing functional problems such as standing up from a chair, that may be much more important to the person, and that may indeed lead to future readmissions and prolonged hospitalization [40]. This affirms the need for person-centered, rather than disease-centered, care for people with multimorbidity throughout the various levels of care within the health system. To ensure that health and rehabilitation services are person-centered and health systems are responsive to rapidly evolving health care demands, there is an urgent need for health systems in LMICs to transit from specialized towards integrated health management models. This would be realized most successfully only if guided by research into multimorbidity epidemiological patterns, associated factors, function, and function-related impact.
Rationale
The global move towards primary care-led chronic disease management [41] has highlighted the identification of multimorbidity patterns and severity (for example measured by functional impairment, activity limitations and/or participation restrictions) as a research priority, given its correlation with patient outcomes [4, 22]. Most countries, including LMICs, are advocating for and making deliberate efforts towards the realization of UHC; the intention being ensuring access to quality and effective health services, without undue financial hardship.
In LMICs, the goal of UHC may unfortunately be hard to realize regarding patients with multimorbidity, as the health systems are not equipped to deal with complex chronic conditions [34]. The management of patients with multimorbidity provide significant challenges to health- and rehabilitation specialists. Existing clinical guidelines for multimorbidity management [42–44] hail from HICs, making application in LMIC context inappropriate. Furthermore, these guidelines mostly use count-based definitions of multimorbidity. This is problematic, as the same number but different types of chronic diseases will likely have different risk profiles, treatment needs, and outcomes [11].
Evidence about patterns of chronic conditions that tend to cluster together in low-resource populations and have the greatest impact on person-important outcomes such as function, and teasing out modifiable risk factors and pathways that may be common to multimorbidity and functional status, would contribute towards the development of locally-relevant person-centered practice guidelines tailored to the needs of people with specific multimorbidity patterns. Ultimately, improved understanding of the needs and functional outcomes of individuals with different multimorbidity patterns will enable the transition from disease-centered to person-centered care for those living and aging with multimorbidity [11]. As quality of care would improve and the financial burden associated with multimorbidity and functional decline likely lessen, this would be an important step towards attaining UHC in LMICs.
Aim of the planned scoping review
The aim of the planned scoping review is to provide an overview of the scope and nature of the existing literature on associations between multimorbidity patterns and function in adults, specifically in the context of LMICs. Through conducting a systematic search of peer-reviewed literature to scope the field, mapping the study characteristics, themes and methodologies used in existing literature and subsequently identifying limitations and evidence gaps, we hope to provide recommendations to guide future research on multimorbidity patterns and functional associations in the context of low-resource countries.