Low Vasopressin in Myalgic Encephalomyelitise/Chronic Fatigue Syndrome

The complex clinical picture of myalgic encephalomyelitis (ME)/chronic fatigue syndrome (CFS) includes orthostatic intolerance with symptoms and signs suggesting abnormal water homeostasis and hypovolemia. Since many ME/CFS patients report polyuria-polydipsia, we conducted an observational study based on series of plasma and urine osmolality (P-Osm and U-Osm) as well as plasma levels of vasopressin (P-VP) or copeptin in consecutive patients diagnosed with ME/CFS according to the International Consensus Criteria.

P-VP as well as P-Osm and U-Osm were measured in 111 patients after 10 h overnight fasting and fluid deprivation. Additional 13 patients were assessed for copeptin, when P-VP measurements were no longer available. The clinical routine also included brain MRI and blood chemistry.

P-Osm was abnormally high (>292 mOsm/kg) in 71 of 124 (57.3%) and U-Osm below the reference interval (<750 mOsm/kg) in 82 of 124 (66.1%) patients. P-VP was below the level of detection (<1.6 pg/mL) in 91 of 111 (82.0%) patients. A normal P-VP level compared with their P-Osm was found in 11 of 111 (9.9%) patients. Copeptin levels were all within the given reference range, albeit in the lower end in most patients. No indication of relevant pathology in either hypothalamus or hypophysis was present.

Our findings suggest that chronic down-regulation of VP mimicking central diabetes insipidus is an important measurable part of the disease mechanism that potentially contributes to criterial symptoms of ME/CFS.