A 32-year-old man was referred for investigation of intractable hypercapnia after ICU hospitalization for acute hypercapnic respiratory failure. The patient was a heavy smoker and had an unremarkable medical history until 3 months earlier when progressive fatigue and morning headaches developed. He was then prescribed the noradrenergic and specific serotonergic ant depressive agent mirtazapine. All routine lab test results were within normal limits. Arterial blood gases analysis revealed hypoxemia with hypercapnia. Spirometry showed mild obstructive pulmonary disease (, whereas chest X-rays and mouth pressures were.
Upon admission, neurological examination revealed lower cranial nerve palsies with a bilaterally absent gag reflex and decreased sensation at the back of the oropharynx. On the elevation of the soft palate, the uvula deviated to the left side, and there was mild hypophonia and difficulty in swallowing. The right trapezius and the right side of the tongue were atrophic and weak. Upper limb examination revealed bilaterally absent tendon reflexes with mildly reduced pinprick sensation on the left. Lower limb testing showed mild weakness on the left and increased tendon reflexes bilaterally with extensor plantar response on the left and equivocal response on the right. Cerebellar testing revealed titubation, a positive Romberg’s sign, and inability to perform tandem gait. Overnight polysomnography was performed. The study demonstrated a severe and complexly altered respiratory function, characterized by a mixed type of apnoeic episodes, predominately obstructive. Magnetic resonance imaging (MRI) of the head was done. To elucidate the mechanisms underlying the patient’s respiratory insufficiency, we studied the corticodiaphragmatic pathway with transcranial magnetic stimulation (TMS). Representative waveforms are presented in the image.
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