From the Guidelines

Delirium and depression are two distinct clinical entities that can present with overlapping symptoms, making differential diagnosis challenging.

Acute Onset: Delirium is characterized by an acute onset and fluctuating course, often accompanied by altered level of consciousness, disorganized thinking, and impaired attention 1.
Altered Level of Consciousness: Delirium is marked by a disturbed level of consciousness, with a reduced ability to focus, sustain, or shift attention 1.
Cognitive Disturbances: Delirium involves cognitive disturbances, such as inattention, disorganized thinking, and memory deficits 1.

Delirium Management: Delirium is often managed with haloperidol (0.5-2 mg orally or intravenously every 2-4 hours as needed) or quetiapine (12.5-50 mg orally every 4-6 hours as needed) 1.
Depression Treatment: Depression is typically treated with selective serotonin reuptake inhibitors (SSRIs) such as sertraline (50-200 mg orally daily) or fluoxetine (20-60 mg orally daily) for a minimum of 6-8 weeks.

Thorough Assessment: A thorough assessment of the patient's mental status, medical history, and laboratory results is essential to distinguish between delirium and depression 1.
Validated Assessment Scales: Validated assessment scales, such as the Richmond Agitation Sedation Scale and Glasgow Coma Scale, may be employed to objectively quantify the severity of symptoms 1.

From the Research

Delirium and depression are two distinct mental health conditions that can be difficult to differentiate due to overlapping symptoms 2, 3, 4.
Delirium is characterized by an acute disturbance of consciousness, attention deficit, and change in cognitive function, whereas depression is an affective disorder marked by a dysphoric mood and loss of interest in activities 3, 5.
The two conditions can coexist, and patients with delirium may also exhibit depressive symptoms, making diagnosis challenging 2, 4.

Delirium and depression share common risk factors, such as age, frailty, and multimorbidity, which can contribute to the development of both conditions 5, 6.
Patients with a history of depression are more likely to develop delirium, and conversely, delirium can increase the risk of developing depression 4, 6.
The clinical overlap between delirium and depression highlights the importance of careful assessment and diagnosis to provide optimal care for patients with these conditions 2, 3, 4.

A comprehensive evaluation, including laboratory tests and imaging studies, is necessary to diagnose delirium and depression accurately 3, 5.
Validated screening methods, such as the Confusion Assessment Method, can help diagnose delirium 5.
Treatment for delirium and depression may involve pharmacological and non-pharmacological interventions, including reorientation, early mobilization, and sleep improvement 5.
Careful drug selection and monitoring are crucial when using pharmacological treatments, especially in patients with delirium 5.

Depression symptom burden and worsening trajectory can predict delirium risk during hospitalization, highlighting the importance of monitoring and addressing depressive symptoms 6.
Increased awareness of subclinical depression symptoms may be warranted for delirium prevention, particularly in older adults 6.
Multimodal, non-pharmacological treatments, such as reorientation and early mobilization, can help prevent delirium in high-risk patients 5.