Serum calcium to magnesium ratio as a prognostic biomarker of three-month recovery in Bell’s palsy: a prospective cohort study

Bell’s palsy is the most common cause of acute peripheral facial paralysis. Although the majority of patients recover satisfactorily, approximately 30% experience delayed or incomplete recovery, resulting in significant functional and psychosocial consequences. Magnesium (Mg) has a neuroprotective effect and acts as a physiological antagonist of calcium (Ca). The calcium-magnesium balance has not previously been investigated in Bell’s palsy. We assessed whether the baseline serum Ca/Mg ratio was associated with favourable versus unfavourable recovery at three months. In this single-centre prospective cohort study, 149 adults with idiopathic Bell’s palsy were analysed. Before initiating corticosteroid therapy, serum calcium, magnesium, and albumin levels were measured. Corrected calcium was calculated from measured total calcium, and the Ca/Mg ratio was determined in both mass-based and molar units. Recovery was graded using the House-Brackmann (HB) scale; delayed recovery was defined as an HB score > II at the third month. The groups were compared, and the discriminatory performance of the ratio was assessed using receiver operating characteristic (ROC) analysis and multivariate logistic regression. Seventy-seven patients (51.7%) achieved favourable recovery (HB ≤ II) and 72 (48.3%) had unfavourable recovery. The corrected Ca/Mg ratio was significantly higher in the unfavourable recovery group (4.80 [4.53–5.09] vs. 4.31 [4.06–4.51]; P < 0.001). The corrected ratio discriminated unfavourable recovery with an AUC of 0.846 (95% CI, 0.784–0.902), demonstrating significantly better discrimination than corrected calcium (ΔAUC, 0.175; DeLong P < 0.001) and magnesium (ΔAUC, 0.085; P = 0.003). At the Youden-optimal cutoff of 4.39, sensitivity was 90.3% and specificity was 66.2%. In the multivariable analysis, the corrected Ca/Mg ratio remained independently associated with unfavourable recovery at three months (adjusted OR, 8.84 per 1-SD increase; 95% CI, 4.08–19.15; P < 0.001). A higher pretreatment albumin-corrected serum Ca/Mg ratio was independently associated with unfavourable recovery at three months in Bell’s palsy and demonstrated significantly better discrimination than corrected calcium or magnesium alone. The ratio is a promising and readily available prognostic biomarker; but, external validation is required before clinical adoption.