The role of hypoglycorrhachia as a cerebrospinal fluid to serum glucose ratio in adults with encephalitis

Objective

We aimed to determine the clinical and prognostic significance of hypoglycorrhachia in adults with encephalitis.

Methods

We conducted an IRB-approved, retrospective chart review of adult patients diagnosed with encephalitis from Greater Houston and Baltimore regions from 2005 to 2022 based on the 2013 International Encephalitis Consortium criteria. Data was collected on demographics, presenting symptoms, diagnostic findings, and clinical outcomes. Hypoglycorrhachia was defined as a cerebrospinal fluid (CSF) to serum glucose ratio ≤ 0.6. Patients were dichotomized based on presence or absence of hypoglycorrhachia.

Results

Of 556 patients (47.5 % infectious, 15.6 % seropositive autoimmune, 36.9 % unknown etiology), 69.8 % had hypoglycorrhachia (n = 388). Patients with hypoglycorrhachia were more often immunocompromised and presented with fever, headache, nausea, and neck stiffness (p < 0.05), while patients without hypoglycorrhachia more frequently presented with seizures, memory deficits, and psychiatric symptoms (p < 0.05). Hypoglycorrhachia was associated with CSF pleocytosis (CSF white blood cell level ≥ 5 cells/μL), a higher CSF protein level (p < 0.05), and infectious etiology. Absence of hypoglycorrhachia was associated with seropositive autoimmune etiology, greater use of immunotherapies, higher intensive care unit (ICU) admission rates, and longer hospitalization (p < 0.05). Prevalence rates and etiology distribution of patients with hypoglycorrhachia were comparable to those in a subset of patients with concomitant CSF/serum glucose collection.

Conclusions

Hypoglycorrhachia is strongly associated with bacterial and fungal etiologies and their clinical features, while absence of hypoglycorrhachia is linked to higher ICU admission rates and prolonged hospitalization, likely due to autoimmune encephalitis. The CSF/serum glucose ratio captures greater variability in serum glucose levels yet reliably rules out absolute hypoglycorrhachia when >0.6, regardless of concomitant collection.