What is the most likely diagnosis for a 71-year-old woman with hypertension and hypothyroidism who awakens around 2:30 am, cannot return to sleep, has reduced sleep efficiency, a normal apnea‑hypopnea index, and no depressed mood?

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Advanced Sleep-Wake Phase Disorder (ASWPD)

The most likely diagnosis is advanced sleep-wake phase disorder (option d). This 71-year-old woman presents with a classic constellation of findings: habitual early evening sleep onset (falling asleep at 6 PM despite preferring 9 PM), early morning awakening (2:30 AM) with inability to return to sleep, and significant social impairment due to the phase advance—all hallmark features of ASWPD.

Clinical Reasoning

Why ASWPD is the Primary Diagnosis:

The patient's sleep pattern demonstrates a phase advance of approximately 3 hours from her preferred schedule. She experiences:

  • Involuntary sleep onset in early evening (6 PM)
  • Consistent early morning awakening (2:30 AM)
  • Total sleep duration that appears adequate (approximately 8.5 hours if sleeping 6 PM to 2:30 AM)
  • Functional impairment from missing evening social activities—a critical diagnostic criterion
  • Age-appropriate presentation (ASWPD increases with advancing age)

Ruling Out Alternative Diagnoses:

Not Insomnia (option a): While she has difficulty maintaining sleep after 2:30 AM, this is not primary insomnia. True insomnia involves difficulty initiating or maintaining sleep at the desired bedtime. Her problem is that her circadian rhythm is advanced—she can sleep, just at the wrong time. The reduced sleep efficiency of 68% on PSG reflects her circadian misalignment, not an intrinsic sleep disorder.

Not REM-Related OSA (option b): The PSG definitively excludes this:

  • AHI of 2.4/hr is normal (threshold for OSA is ≥5)
  • REM index of 3.8/hr is also below diagnostic threshold
  • Lowest oxygen saturation of 90% is minimally abnormal and insufficient to explain her symptoms
  • Her sleep disruption pattern (early morning awakening) doesn't correlate with REM sleep timing

Not Depression (option c): She explicitly denies sad mood. While early morning awakening can be a vegetative symptom of depression, it typically occurs at 3-5 AM (not 2:30 AM consistently) and is accompanied by other depressive symptoms including anhedonia, which she lacks—she wants to participate in evening activities but cannot stay awake.

Thyroid Function Considerations:

Her thyroid function is adequately treated:

  • TSH 3.2 mIU/L (normal range)
  • Free T4 1.0 ng/dL (normal range: 0.8-1.8)
  • She's on levothyroxine maintenance

While hypothyroidism can affect sleep architecture 1, 2, 3, her treated thyroid status makes this an unlikely primary contributor. The research showing associations between hypothyroidism and sleep disorders 3, 4, 5 primarily involves untreated or subclinical hypothyroidism with elevated TSH levels, which doesn't apply here.

Clinical Pitfalls to Avoid:

  1. Don't over-interpret minimal PSG abnormalities: The slightly reduced sleep efficiency and minimal oxygen desaturation are consequences of circadian misalignment, not primary pathology requiring treatment

  2. Don't confuse circadian rhythm disorders with insomnia: The key distinguishing feature is that ASWPD patients can sleep well when aligned with their advanced rhythm—they just can't sleep at socially conventional times

  3. Don't attribute everything to age: While older adults naturally experience some phase advance, this degree of impairment warrants diagnosis and treatment

  4. Don't miss the functional impairment: Her distress about missing social activities is what elevates this from normal aging to a disorder requiring intervention

Management Approach:

Treatment for ASWPD focuses on phase delay strategies:

  • Bright light therapy in the evening (7-9 PM) to delay circadian phase
  • Chronotherapy: gradually delaying bedtime in 15-30 minute increments
  • Melatonin in the morning (controversial, limited evidence)
  • Maintaining consistent sleep-wake schedule once optimal timing achieved
  • Avoiding bright light in early morning hours

The goal is to shift her circadian rhythm later to align with her desired 9 PM bedtime and allow her to participate in evening social activities, thereby improving her quality of life.

References

1
Research

Thyroid Dysfunction and Sleep Disorders.

Frontiers in endocrinology, 2021

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