Infections to the Central Nervous System (CNS) are notable for their diversity; Infections that affect the CNS can be catastrophic and potentially lethal. They range from common to rare, acute to chronic, benign to fatal. Although some are self-limited or are easily cured with modern treatment, others are relentlessly progressive despite treatment, or have no known treatment. Central nervous system infections (CNS) limited to the meninges or with brain parenchyma involvement are common causes of hospital admissions. Infection of the central nervous system (CNS) can be viral, bacterial, fungal, or parasitic in origin. Infectious microorganisms most often enter the CNS by direct penetration after trauma or by travelling in the bloodstream. People who are immune compromised from conditions such as AIDS, cancer, steroid use, diabetes or alcoholism may be at risk for opportunistic infections which would not ordinarily affect persons with normal immune defenses. Sodium disorders are associated with considerable morbidity and mortality. Hyponatremia is a common electrolyte disturbance and is a common finding in patients with acute cerebral insult.
Hyponatremia in CNS infection could be due to two mechanisms, first one is Syndrome of Inappropriate Anti Diuretic Hormone secretion (SIADH) and other one is Cerebral Salt wasting syndrome (CSW). SIADH is a volume-expanded state because of antidiuretic hormone-mediated renal water retention. CSW is characterized by a contracted effective arterial blood volume (EABV) resulting from renal salt wasting. Making an accurate diagnosis is important because the treatment of each condition is quite different.