Optic Neuritis Presented as Syndrome of Inappropriate Antidiuretic Hormone Secretion in an 8 Year Old.

Optic neuritis is a rare demyelinating disorder, which involves the optic nerve. It can be a monophasic self-limiting illness due to postinfectious or postvaccination etiology. It can also be an initial presentation of a relapsing demyelinating disorder such as multiple sclerosis or neuromyelitis optica spectrum of disorders. It is characterized to aquaporin-4 antibody-rich areas in the brain, optic nerve, and spinal cord. The hypothalamus and periventricular area are also rich in specific antibodies and may lead to dysfunction in the hypothalamic-pituitary axis. Antidiuretic hormone (ADH) is synthesized in the hypothalamus and stored in the posterior pituitary and may secrete inappropriately due to this disturbance. This will impair water excretion from the kidney, leading to hyponatremia. When hyponatremia is significant, the patient will present with confusion, agitation, and convulsions. This case report discusses acute symptomatic hyponatremia as the initial presentation of optic neuritis due to syndrome of inappropriate ADH secretion (SIADH).