To report a case of osmotic demyelinating syndrome (ODS) secondary to chemotherapy for breast cancer. 

ODS comprises both central pontine demyelination and extrapontine myelinolysis. This condition accounts for 0.4% to 0.56% of neurological admissions to tertiary referral hospitals and 0.06% of medical admissions. Although rapid correction of hyponatremia is the most common cause, other etiologies such as alcohol consumption, chronic renal failure, and organ transplantation are also reported. Chemotherapy can be an infrequent cause of this condition. Here we describe a case of ODS in a normonatremic patient in treatment with trastuzumab, pertuzumab, and docetaxel. 

 ODS could be associated with combination chemotherapy treatment in the setting of a normonatremic patient. In 2014, Sungjae Lee and colleagues reported a similar case in a patient with colon cancer who received 5-fluorouracil, oxaliplatin, and leucovorin chemotherapy. In another study published by Cortes and colleagues, the development of osmotic demyelinating syndrome when using a combination of trastuzumab and pertuzumab for breast cancer was reported as a rare finding (one case of twenty-nine patients). To our knowledge, this is one of the first cases describing an ODS following therapy with pertuzumab, trastuzumab, and docetaxel.