Cytotoxic Lesions of the Corpus Callosum Associated With Addison's Disease: A Case Report.

Cytotoxic Lesions of the Corpus Callosum (CLOCCs) are transient splenial lesions typically triggered by infections, trauma, or metabolic disturbances. This report documents a unique case of a 13-year-old girl with CLOCCs secondary to Addison's disease, an association not previously reported. The patient initially presented with lethargy, fever, and hyperpigmentation of the skin and gingiva. Investigations revealed profound hyponatremia (121 mmol/L) and hypoosmolality, while a brain MRI confirmed a cytotoxic lesion in the splenium. Although meningoencephalitis was initially suspected, markedly elevated adrenocorticotropic hormone (ACTH) and low cortisol levels ultimately confirmed primary adrenal insufficiency. The pathogenesis likely involves cytotoxic edema and blood-brain barrier dysfunction driven by severe electrolyte imbalance and hypocortisolism. Following hydrocortisone replacement therapy and gradual sodium correction, the patient achieved a rapid clinical recovery. A follow-up MRI demonstrated complete resolution of the lesion within one week. This case highlights the importance of considering adrenal insufficiency in the differential diagnosis of reversible splenial lesions, particularly when physical signs like hyperpigmentation are present.