Background: Hypomagnesemia is commonly encountered in patients with a wide variety of diseases including subarachnoid hemorrhage (SAH), cardiovascular emergencies, head trauma, migraine attacks, seizure and preeclampsia. It seems to be associated with a poor clinical outcome. This study considers the prevalence and temporal distribution of hypomagnesemia after aneurysmal SAH and its correlation with the severity of SAH, delayed cerebral ischemia (DCI) as well as the neurological outcome after a period of three months.

Methods: Between 2003 and 2008, 60 patients were admitted to the emergency ward of Imam Khomeini Hospital with acute SAH. Serum magnesium levels were measured during the first 72 hours, days 4-7, and second and third weeks after SAH. The three-month outcome was assessed according to the Glasgow Outcome Scale (GOS). Clinical SAH grading was performed according to the criteria of the World Federation of Neurological Surgeons (WFNS) and the patients were allocated to "Good" (GOS = 4, 5) and "Poor" (GOS= 1-3) outcome groups. The prevalence of hypomagnesemia was assessed in both patient groups. Fisher exact test was used to analyze data.

Results: Hypomagnesemia occurred in 22% of patients during the first 72 hours after SAH. It was associated with more prevalent DCI (p<0.05), whereas low serum magnesium levels during days 4-7 17% of patients) and the second week (22% of patients) after SAH were correlated with poor clinical outcome (p<0.05). No correlation was found between first 72 hour-hypomagnesemia and poor clinical outcome at three months.

Conclusion: Hypomagnesemia occurs after aneurysmal SAH and it may predict the occurrence of DCI, while low serum magnesium levels during days 4-7 and within the second week of event predict poor clinical outcome at three months. Treatment of this electrolyte disturbance may have a favourable effect on the clinical outcome of patients with aneurysmal SAH.