What is the diagnosis for an elderly patient with Alzheimer dementia who has trouble falling asleep, wanders at night, and has multiple periods of sleep and wakefulness throughout the day?

Diagnosis: Irregular Sleep-Wake Rhythm Disorder (ISWRD)

The diagnosis is irregular sleep-wake rhythm disorder (ISWRD), characterized by the absence of a clear circadian sleep-wake pattern, with multiple 2-3 hour sleep bouts distributed throughout the 24-hour period, normal total sleep time (7-8 hours), and occurring in the context of Alzheimer dementia. 1

Key Diagnostic Features Present

This patient demonstrates all the hallmark features of ISWRD:

• Lack of consolidated circadian pattern: Multiple sleep periods of 2-3 hours occurring both day and night, with no single major sleep episode 1
• Variable timing: Sleep onset differs from day to day, confirming the irregular nature rather than a consistent phase shift 1
• Normal total sleep time: Averages 7-8 hours per 24-hour period, which is within normal range despite fragmentation 1
• Documentation requirement met: Sleep diaries and actigraphy showing at least 3 sleep bouts over 7+ days 1
• Associated condition: Alzheimer dementia, the most common underlying condition for ISWRD 1

Why Other Diagnoses Are Incorrect

Advanced sleep-wake phase disorder (ASWPD) is excluded because:

• ASWPD presents with a consistent early sleep onset (falling asleep before desired time) and early morning awakening 1
• This patient has variable sleep timing, not a consistently advanced phase 1
• ASWPD patients have consolidated sleep during their advanced phase, not fragmented multiple sleep bouts 1

Delayed sleep-wake phase disorder (DSWPD) is excluded because:

• DSWPD shows a consistent delay in sleep onset with difficulty falling asleep at conventional times 1
• The patient's late evening wakefulness is not consistent—sleep timing varies day to day 1
• DSWPD features consolidated sleep during the delayed period, not multiple short bouts 1

Insomnia disorder is excluded because:

• Insomnia involves difficulty initiating or maintaining sleep with reduced total sleep time 1
• This patient achieves normal total sleep time (7-8 hours per 24 hours) 1
• The problem is distribution of sleep across the 24-hour period, not insufficient sleep 1

Non-24-hour sleep-wake rhythm disorder (N24SWD) is excluded because:

• N24SWD requires progressive delay (or advance) of sleep-wake times showing a clear drift pattern 1
• This patient has variable timing without progressive drift 1
• N24SWD diagnosis requires 14+ days of documentation showing the progressive shift, and typically occurs in blind individuals 1

Pathophysiology in Alzheimer Dementia

The development of ISWRD in this patient likely results from:

• Suprachiasmatic nucleus (SCN) degeneration: Alzheimer disease causes decreased neurons within the SCN, the brain's master circadian pacemaker 1
• Reduced zeitgeber exposure: Decreased exposure to bright light and structured social/physical activities weakens circadian synchronization 1, 2
• Loss of circadian amplitude: The combination of SCN pathology and reduced environmental cues results in loss of consolidated sleep-wake rhythms 1, 2

Clinical Implications

ISWRD poses significant challenges for caregivers due to unpredictable sleep patterns and nighttime wandering 1. The disorder is most commonly encountered in institutionalized dementia patients but also occurs in community-dwelling individuals with neurodegenerative disease 1.