A team of researchers from the United States presented the case of a patient with neuromyelitis optica spectrum disorder (NMOSD) with atypical presentation, such as syndrome of inappropriate antidiuretic hormone secretion (SIADH), which has sometimes been associated with the disease.

“This case illustrates the importance of looking for syndromes, such as SIADH,” the researchers wrote in the journal Neurology. “This can guide diagnostic testing, such as getting thin MRI cuts through the hypothalamus and brainstem, as well as advanced management techniques such as immunotherapy,” they added.

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The case is that of a 35-year-old female with antiaquaporin 4 (AQP4) antibody-positive NMOSD who presented with 2 weeks of lightheadedness, generalized weakness, and urinary frequency.

She was treated with 3 liters of normal saline, but this led to limited improvement in her serum sodium. She was diagnosed with new-onset hyponatremia.

Workup of her hyponatremia showed low serum and high urine osmolality, and normal urinary sodium, overall consistent with SIADH. 

Because of her history of aggressive NMOSD with recurrent relapses, hypothalamic involvement was suspected, which was confirmed with a brain MRI. 

She was treated with 1 g of intravenous methylprednisolone daily for 3 days and 5 sessions of plasma exchange. She was also put on rituximab therapy. Her sodium level was slowly corrected with hypertonic 3% saline, and her hyponatremia was resolved leading to an improvement in her symptoms.

SIADH is characterized by the body making too much antidiuretic hormone. The condition can be caused by NMOSD lesions in the hypothalamus and the circumventricular organs surrounding the 3rd and 4th ventricles, which serve as osmoregulator. SIADH is 1 of the most common causes of hyponatremia. Its initial management involves fluid restriction. However, in the case of  NMOSD-related disease, the ultimate management is immunotherapy.


Brayo P, Serrano E, Thakkar RS, Osborne B. Pearls & oysters: syndrome of inappropriate antidiuretic hormone secretion presenting as neuromyelitis optica spectrum disorder flare. Neurology. Published online July 24, 2023. doi:10.1212/WNL.0000000000207178