Stage IIIB non-squamous NSCLC on chemoimmunotherapy: alcohol-related hypertonic hyponatremia corrected during oncology follow-up

What happened, in summary

This 56-year-old man had Stage IIIB non-squamous non-small-cell lung cancer diagnosed about 1 year before the case presentation. He was receiving combination chemoimmunotherapy with pemetrexed, pembrolizumab, and carboplatin every 3 weeks. His medical history was complex and included dilated cardiomyopathy, coronary artery disease, type 2 diabetes, chronic kidney disease, chronic hepatitis B infection, and prior partial gastrectomy. He smoked 10-12 cigarettes daily and initially said he did not drink much alcohol. Over 3 months, he had 3 episodes of dizziness, each accompanied by severe low serum sodium below 120 mmol/L. He had no headache, seizure, vomiting, diarrhea, excessive thirst, or weight loss. Because lung cancer can be associated with SIADH, that diagnosis was considered, especially because he had a previous episode with low osmolality and urinary findings compatible with mild SIADH. However, the more recent episodes were different: measured serum osmolality was high, and the osmolar gap was markedly elevated at 80 mOsm/kg. Ethanol testing later showed a serum ethanol level of 36 mmol/L, and he then acknowledged daily excess alcohol intake in the preceding months. He was hospitalized for alcohol detoxification with a reducing chlordiazepoxide regimen, vitamin B complex, and oral thiamine. He was referred for alcohol cessation support but preferred self-management. Over 6 months, he gradually stopped alcohol use. His serum ethanol disappeared, the osmolar gap resolved, and sodium levels improved while he continued oncology follow-up. The cancer treatment status remained ongoing, but the dangerous electrolyte abnormality improved once the alcohol-related osmolar gap was recognized and addressed.