Delirium mimicking psychiatric relapse in older adults: a case-based analysis of diagnostic bias

Background

Diagnosing acute psychiatric deterioration in older adults remains particularly challenging due to age-related physiological changes, multimorbidity, and atypical clinical presentations. Delirium is frequently under-recognised—especially in hypoactive forms—and may closely mimic relapse of a primary psychiatric disorder. However, the challenge is not solely one of recognition, but of clinical interpretation. In complex presentations, salient affective symptoms may overshadow less conspicuous disturbances in attention and cognition, leading to diagnostic misattribution and delayed identification of underlying medical conditions.

Objectives

To illustrate how a form of affective bias in diagnostic reasoning may influence clinical judgement in late-life psychiatry, and to highlight key phenomenological features that support differentiation between delirium and primary affective relapse.

Methods

We present the case of a 76-year-old man with a history of recurrent depressive disorder, previously stable under maintenance treatment, referred for urgent psychiatric assessment due to suicidal ideation and apparent depressive decompensation. Clinical evaluation emphasised temporal onset, qualitative analysis of cognitive and language disturbances, and identification of potential medical precipitants, complemented by collateral history.

Results

The patient presented with acute-onset emotional distress, insomnia, and ruminative ideation suggestive of depressive relapse. However, closer examination revealed a discordant neurocognitive profile: attention was capturable but poorly sustained, short-term memory was impaired, and speech was circumstantial, with occasional pararresponses and reduced coherence. These features, together with the abrupt onset and fluctuating course, raised suspicion of delirium. Although structured tools such as the Confusion Assessment Method may support detection, their application presupposes that delirium is actively considered in the differential diagnosis. In this case, the prominence of affective symptoms risked diverting attention from core cognitive features. Collateral history identified recent urinary symptoms, and investigations confirmed a urinary tract infection. Following treatment of the underlying condition, there was rapid resolution of both cognitive and affective symptoms, without the need to modify psychotropic medication.

Discussion

This case illustrates a common yet under-recognised diagnostic error in geriatric psychiatry, whereby affective symptoms disproportionately shape clinical judgement. This affective bias may obscure disturbances in attention, cognition, and language that are more indicative of delirium. In older adults, reduced cognitive reserve, polypharmacy, and increased physiological vulnerability contribute to overlapping clinical syndromes in which delirium may present with prominent emotional or behavioural features. Crucially, the difficulty lies not in the absence of diagnostic tools, but in the prioritisation of clinical signals: when affective distress appears compelling, more subtle but diagnostically decisive features may be underexplored. Differentiation depends less on the presence of specific symptoms and more on their structure and temporal dynamics. Attentional dysfunction, fluctuation, and disorganisation of thought and language remain key signals.

Conclusions

Accurate differentiation between delirium and psychiatric relapse in older adults requires a shift from symptom-based to process-oriented clinical reasoning. Recognising and counteracting affective bias may improve diagnostic precision and ensure timely identification of reversible medical conditions, with direct implications for patient safety and clinical outcomes.

References

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