{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,28]],"date-time":"2026-09-28T17:16:33Z","timestamp":1790615793787,"version":"4.1.0"},"reference-count":22,"publisher":"BMJ","issue":"9","content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["BMJ Case Rep"],"accepted":{"date-parts":[[2026,9,8]]},"published-print":{"date-parts":[[2026,9]]},"abstract":"<jats:p>A man in his 40s with morbid obesity and type 2 diabetes mellitus presented with early-morning drowsiness and respiratory distress after several days of nocturnal dyspnoea and unsupervised loop diuretic use. Initial assessment showed hypoglycaemia, acute-on-chronic hypercapnic respiratory acidosis with metabolic alkalosis and obstructive ventilatory mechanics, requiring intubation. Within 24 hours of extubation, he re-presented with recurrent drowsiness and striking bilateral cerebellar ataxia despite normal neuroimaging. Repeat arterial blood gases again demonstrated acute-on-chronic hypercapnic respiratory failure, and his encephalopathy and cerebellar signs resolved completely with ventilatory support and correction of PaCO\u2082. Subsequent high-resolution CT of the chest showed aspiration-related consolidation without underlying parenchymal lung disease and polysomnography confirmed severe obstructive sleep apnoea. This case illustrates hypercapnic encephalopathy presenting as reversible bilateral cerebellar ataxia in the context of diuretic-associated metabolic alkalosis and suspected chronic CO2 retention and highlights the need for early arterial blood gas analysis and careful interpretation of ventilator waveforms.<\/jats:p>","DOI":"10.1136\/bcr-2026-273356","type":"journal-article","created":{"date-parts":[[2026,9,28]],"date-time":"2026-09-28T16:31:01Z","timestamp":1790613061000},"page":"e273356","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":0,"title":["Reversible bilateral cerebellar ataxia resulting from hypercapnic encephalopathy in an undiagnosed patient with obstructive sleep apnoea"],"prefix":"10.1136","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3729-8608","authenticated-orcid":false,"given":"Arihant","family":"Jain","sequence":"first","affiliation":[{"name":"Department of Emergency Medicine, All India Institute of Medical Sciences, New Delhi, DL, India"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nayer","family":"Jamshed","sequence":"additional","affiliation":[{"name":"Department of Emergency Medicine, All India Institute of Medical Sciences, New Delhi, DL, India"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Falgun","family":"Maheriya","sequence":"additional","affiliation":[{"name":"Department of Emergency Medicine, All India Institute of Medical Sciences, New Delhi, DL, India"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"239","published-online":{"date-parts":[[2026,9,28]]},"reference":[{"key":"2026092809300940000_19.9.e273356.1","doi-asserted-by":"crossref","first-page":"389","DOI":"10.1097\/00005792-195612000-00003","article-title":"Carbon dioxide intoxication: the clinical syndrome, its etiology and management with particular reference to the use of mechanical respirators","volume":"35","author":"SIEKER","year":"1956","journal-title":"Medicine (Baltimore)"},{"key":"2026092809300940000_19.9.e273356.2","doi-asserted-by":"crossref","first-page":"829","DOI":"10.7326\/0003-4819-63-5-829","article-title":"Hypercapnia: mental changes and extrapulmonary complication. 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