From Headache to Altered Consciousness: Headache Attributed to Hypoxia and/or Hypercapnia in a Smoker With Undiagnosed Chronic Obstructive Pulmonary Disease.

We present the case of a 57-year-old male with a history of smoking, hypertension, dyslipidemia, and migraines who experienced a one-month history of dyspnea and headaches, followed by sudden-onset altered consciousness. Initial imaging ruled out cerebrovascular and infectious etiologies, and arterial blood gas analysis revealed severe hypercapnia and hypoxemia (partial pressure of arterial carbon dioxide: 117 mmHg, partial pressure of arterial oxygen: 111 mmHg under a 10 L/min oxygen mask). The patient's condition improved with mechanical ventilation, resulting in the resolution of both altered consciousness and headaches. Magnetic resonance angiography (MRA) demonstrated cerebral vasodilation, which normalized after treatment, confirming hypercapnia as the underlying cause. This case highlights the diagnostic challenges of differentiating headaches attributed to hypoxia and/or hypercapnia, particularly in smokers. MRA findings of cerebral vasodilation in the context of hypercapnia may provide a diagnostic clue.