The co-occurrence of Guillain-Barré syndrome and inappropriate ADH syndrome in a Rheumatoid arthritis patient

Rheumatoid Arthritis (RA) is the most frequently seen connective tissue disorder. In RA, the peripheral nervous system involvements including distal sensory or sensorimotor polyneuropathy and entrapment neuropathies are more common than the central nervous system involvements. Guillain-Barré syndrome (GBS), an autoimmune disorder, can be encountered in any age groups. The syndrome of inappropriate secretion of ADH (SIADH) is characterized by the non-physiologic release of ADH, resulting in impaired water excretion with normal sodium excretion that causes hyponatremia. Herein, we present the co-occurrence GBS and SIADH in a RA patient treated with Methotrexate (Mtx). A 57 year-old female developed ascending weakness, starting from the legs and spreading to the arms while having pneumonia. Electromyography findings were consistent with sensorimotor demyelinating polyneuropathy. The laboratory investigations were compatible with SIADH. In conclusion, the SIADH in GBS should be taken into account for RA patients on Mtx.