The research team, led by Tao Chen, Qingyu Sun, and senior author Muireann Irish, analysed data from 432 people diagnosed with clinically probable frontotemporal lobar degeneration (FTLD) or Alzheimer’s disease between 2008 and 2025 at the Brain and Mind Centre in Sydney. Of these, 358 individuals had complete carer burden data and formed the primary analytic cohort, comprising 230 people in the FTLD group and 128 in the Alzheimer’s disease group. The FTLD group spanned the full clinical spectrum, including behavioural variant frontotemporal dementia, left- and right-sided semantic dementia, progressive nonfluent aphasia, progressive supranuclear palsy, and corticobasal syndrome, while the Alzheimer’s group included typical presentations and logopenic progressive aphasia. Diagnoses were reached by multidisciplinary consensus using internationally recognised criteria, and all participants scored at least 40 out of 100 on a standard cognitive screening battery at baseline.

The methodological design of the study is what sets it apart from earlier work. Rather than relying on the Neuropsychiatric Inventory, the instrument used in most previous caregiver studies, the team turned to the Cambridge Behavioural Inventory—Revised, a carer-reported questionnaire whose broader coverage captures behavioural domains that other tools routinely miss. Chief among these is behavioural rigidity, an umbrella term encompassing stereotypies such as excessive hand rubbing, compulsions like relentless hand washing, stereotyped catchphrases, impulsive acts including pathological gambling, hoarding, restricted interests, insistence on sameness, and ritualistic routines. Carer burden itself was measured with the widely used 12-item Zarit Burden Interview, which quantifies the emotional, physical, and role-related demands of caregiving on a scale from 0 to 48.

The statistical approach was equally rigorous. Multivariate regression models predicted carer burden from seven behavioural and psychological symptom domains, adjusting for patient age, sex, education, disease duration, disease severity, and diagnostic category. Missing data were handled through multiple imputation by chained equations, and the team complemented standardised regression coefficients with relative importance metrics based on the Lindeman–Merenda–Gold method, which partitions explained variance among correlated predictors. This dual strategy allowed the researchers to distinguish symptoms that independently drive burden from those that contribute through shared, synergistic effects with co-occurring behaviours, a nuance that single-coefficient analyses cannot capture.

The headline finding is striking in its clarity. Across the entire dementia cohort, two symptoms emerged as significant predictors of carer burden: behavioural rigidity, with a standardised coefficient of 0.15, and apathy, indexed by the motivation subscale, with a coefficient of 0.14. Both were modest in absolute terms but statistically robust, with confidence intervals excluding zero. Crucially, global cognition, measured by the Addenbrooke’s Cognitive Examination, showed no significant association with carer burden whatsoever. This dissociation is particularly provocative in Alzheimer’s disease, where cognitive decline is conventionally assumed to be the primary engine of carer distress. The data suggest instead that it is the disruption of motivation, behaviour, and daily routine, not the erosion of memory, that most corrodes carer wellbeing.

When the analyses were run separately within diagnostic groups, a syndrome-specific pattern emerged. In the FTLD group, behavioural rigidity was the strongest and most important predictor of carer burden, with a standardised coefficient of 0.18 and the largest relative importance score of 0.137. This finding held even when the researchers excluded participants with behavioural variant frontotemporal dementia, the syndrome most obviously associated with rigid behaviour, indicating that the effect extends across the broader FTLD spectrum. The authors propose a compelling mechanistic account: rigid behaviours are typically high-frequency and resistant to change, forcing carers to organise entire days around accommodating rituals and rules. Over time, this does not merely add to the caregiving workload; it fundamentally reconfigures the carer’s own life, constraining the timing, sequencing, and nature of everyday activities at the expense of efficiency and shared decision-making.

In the Alzheimer’s group, the picture shifted. Here, apathy and abnormal behaviour were the significant predictors, each with a standardised coefficient of 0.26, and apathy carried the largest relative importance value of 0.232. The findings align with qualitative research suggesting that apathy imposes its toll through a subtle but relentless reconfiguration of the caregiving relationship. When a person with dementia loses the drive to initiate activity, responsibility for starting and sustaining every part of daily life falls to the carer, who must navigate the tension between gently steering engagement and preserving the person’s remaining autonomy. That balancing act, the literature suggests, breeds frustration, guilt, and a gradual, painful acceptance of diminished reciprocity in the relationship.

Perhaps the most forward-looking element of the study is its longitudinal component. In 172 participants assessed at baseline and again roughly one year later, the researchers examined how within-person changes in symptoms related to changes in carer burden over the same interval. A single domain stood out: mood-related symptoms, including irritability and agitation, were the only significant longitudinal predictor of increasing carer burden across the combined cohort, with a standardised coefficient of 0.24. No significant longitudinal predictors emerged within either diagnostic group alone, likely reflecting the modest sample sizes and heterogeneous progression rates of individual syndromes. The transdiagnostic pattern, however, is clinically meaningful. Mood-related symptoms fluctuate with situational demands and are notoriously difficult to anticipate, and experience-sampling research has shown that unpredictable and uncontrollable events are potent drivers of negative affect in dementia carers. Even infrequent episodes of agitation, previous work has demonstrated, impose disproportionately high levels of stress, because each episode forces carers to abandon coping strategies that had been working and reallocate their emotional resources.

The clinical implications are direct and actionable. The authors argue that routine screening for behavioural rigidity and apathy should be considered in all patients with dementia, with psychoeducation at the point of diagnosis preparing carers, particularly in Alzheimer’s disease, for apathy as a prominent and burdensome feature rather than a secondary annoyance. In the absence of effective disease-modifying therapies, symptom-focused management may offer the greatest realistic potential for reducing carer burden. Given the well-documented dysfunction of serotonergic and dopaminergic systems in FTLD, and their established links to cognitive flexibility, pharmacological modulation of these pathways may eventually help alleviate rigidity and repetitive behaviours, though current guidelines recommend prioritising non-pharmacological approaches whenever symptoms are mild and pose minimal risk. The study is not without limitations: carer-side factors such as personality, coping style, social support, and hours of care were not modelled, pathological confirmation of diagnosis was unavailable, and the functional rating scale used to index severity has not been validated across every syndrome included. Larger, multi-centre samples with extended follow-up will be needed to refine these syndrome-specific relationships. Yet the core message stands firm. What determines whether a carer buckles under the strain is not how far memory has faded, but whether rigid routines have colonised the household, whether motivation has drained away, and whether mood disturbances are flaring without warning. Recognising these targets, and treating them as the primary clinical outcomes they truly are, may be the most effective way to protect the people who hold dementia care together.

Subject of Research: Behavioural and psychological symptom determinants of carer burden in frontotemporal lobar degeneration and Alzheimer's disease

Article Title: Behavioural and psychological symptom determinants of carer burden across clinical syndromes associated with frontotemporal lobar degeneration and Alzheimer’s disease: a transdiagnostic analysis

Article References: Behavioural and psychological symptom determinants of carer burden across clinical syndromes associated with frontotemporal lobar degeneration and Alzheimer’s disease: a transdiagnostic analysis. (n.d.). https://doi.org/10.1007/s00415-026-14132-1

Image Credits: AI Generated

DOI: 10.1007/s00415-026-14132-1

Keywords: carer burden, dementia, frontotemporal lobar degeneration, Alzheimer's disease, behavioural rigidity, apathy, behavioural and psychological symptoms, Zarit Burden Interview, Cambridge Behavioural Inventory-Revised, caregiving, longitudinal analysis, neuropsychiatry