case_images: PMC11747752_01
case_images: Flow diagram for the approach to the patient with hypotonic polyuria. Abbreviations: AVP-D, arginine vasopressin deficiency; AVP-R, arginine vasopressin resistance; PP, primary polydipsia. 1AVP measurement validated in some countries; 2 Water deprivation test an alternative; 3Actual cutoff depends on reference range of serum Na+; 4Nonosmotic stimulation:for example:acutely unwell/syncope may cause an elevated level. Interpretation of water deprivation test: If copeptin is not available, the indirect water deprivation test can be performed as described by Miller et al. Usually, the concentration of urine over a 16-hour period of fluid restriction is assessed, followed by interpretation of the ability to concentrate urine in response to the synthetic V2 receptor-specific AVP analogue, desmopressin at the end of the test. In patients where the urinary osmolality stays below 300 mOsm/kg during fluid deprivation but increases over 50% upon desmopressin administration, the diagnosis of complete AVP-D can be made. Patients with a persistent low urinary osmolality and no response to desmopressin are diagnosed with AVP-R. Urinary concentration in patients with partial AVP and primary polydipsia is expected to increase to levels above 300 mOsm/kg, whilst remaining below 800 mOsm/kg, with further increases in osmolality seen upon desmopressin injection of more than 9% in partial AVP patients and less than 9% in primary polydipsic patients.
case_images: dgae565f1.jpg
case_images: PMC11747752_03_dgae565f1.jpg
case_images: dgae565-F1
case_images: Subsequent hypertonic saline-stimulated copeptin measurement (with desmopressin omitted on the day of the test) was consistent with AVP-D (serum copeptin 2.3 pmol/L when serum sodium > 150 mmol/L) (Fig. 1). Baseline unstimulated copeptin levels can be used to diagnose AVP-R where patients usually present with a copeptin level >= 21.4 pmol/L (Fig. 1). When copeptin was measured upon hypertonic (3%) saline infusion aiming at a serum sodium level of >= 149 mmol/L, a copeptin value of <= 4.9 mmol/L reliably distinguished patients with AVP-D from patients with PP with a diagnostic accuracy of 97% (Fig. 1).
case_images: PMC11747752_02
case_images: Flow diagram for the approach to the patient with hypotonic polyuria. Abbreviations: AVP-D, arginine vasopressin deficiency; AVP-R, arginine vasopressin resistance; PP, primary polydipsia. 1AVP measurement validated in some countries; 2 Water deprivation test an alternative; 3Actual cutoff depends on reference range of serum Na+; 4Nonosmotic stimulation:for example:acutely unwell/syncope may cause an elevated level. Interpretation of water deprivation test: If copeptin is not available, the indirect water deprivation test can be performed as described by Miller et al. Usually, the concentration of urine over a 16-hour period of fluid restriction is assessed, followed by interpretation of the ability to concentrate urine in response to the synthetic V2 receptor-specific AVP analogue, desmopressin at the end of the test. In patients where the urinary osmolality stays below 300 mOsm/kg during fluid deprivation but increases over 50% upon desmopressin administration, the diagnosis of complete AVP-D can be made. Patients with a persistent low urinary osmolality and no response to desmopressin are diagnosed with AVP-R. Urinary concentration in patients with partial AVP and primary polydipsia is expected to increase to levels above 300 mOsm/kg, whilst remaining below 800 mOsm/kg, with further increases in osmolality seen upon desmopressin injection of more than 9% in partial AVP patients and less than 9% in primary polydipsic patients.
case_images: dgae565f1.jpg
case_images: PMC11747752_03_dgae565f1.jpg
case_images: dgae565-F1
case_images: Subsequent hypertonic saline-stimulated copeptin measurement (with desmopressin omitted on the day of the test) was consistent with AVP-D (serum copeptin 2.3 pmol/L when serum sodium > 150 mmol/L) (Fig. 1). Baseline unstimulated copeptin levels can be used to diagnose AVP-R where patients usually present with a copeptin level >= 21.4 pmol/L (Fig. 1). When copeptin was measured upon hypertonic (3%) saline infusion aiming at a serum sodium level of >= 149 mmol/L, a copeptin value of <= 4.9 mmol/L reliably distinguished patients with AVP-D from patients with PP with a diagnostic accuracy of 97% (Fig. 1).
case_images: PMC11747752_03
case_images: Flow diagram for the approach to the patient with hypotonic polyuria. Abbreviations: AVP-D, arginine vasopressin deficiency; AVP-R, arginine vasopressin resistance; PP, primary polydipsia. 1AVP measurement validated in some countries; 2 Water deprivation test an alternative; 3Actual cutoff depends on reference range of serum Na+; 4Nonosmotic stimulation:for example:acutely unwell/syncope may cause an elevated level. Interpretation of water deprivation test: If copeptin is not available, the indirect water deprivation test can be performed as described by Miller et al. Usually, the concentration of urine over a 16-hour period of fluid restriction is assessed, followed by interpretation of the ability to concentrate urine in response to the synthetic V2 receptor-specific AVP analogue, desmopressin at the end of the test. In patients where the urinary osmolality stays below 300 mOsm/kg during fluid deprivation but increases over 50% upon desmopressin administration, the diagnosis of complete AVP-D can be made. Patients with a persistent low urinary osmolality and no response to desmopressin are diagnosed with AVP-R. Urinary concentration in patients with partial AVP and primary polydipsia is expected to increase to levels above 300 mOsm/kg, whilst remaining below 800 mOsm/kg, with further increases in osmolality seen upon desmopressin injection of more than 9% in partial AVP patients and less than 9% in primary polydipsic patients.
case_images: dgae565f1.jpg
case_images: PMC11747752_03_dgae565f1.jpg
case_images: dgae565-F1
case_images: Subsequent hypertonic saline-stimulated copeptin measurement (with desmopressin omitted on the day of the test) was consistent with AVP-D (serum copeptin 2.3 pmol/L when serum sodium > 150 mmol/L) (Fig. 1). Baseline unstimulated copeptin levels can be used to diagnose AVP-R where patients usually present with a copeptin level >= 21.4 pmol/L (Fig. 1). When copeptin was measured upon hypertonic (3%) saline infusion aiming at a serum sodium level of >= 149 mmol/L, a copeptin value of <= 4.9 mmol/L reliably distinguished patients with AVP-D from patients with PP with a diagnostic accuracy of 97% (Fig. 1).
case_images: Case 3: T1-weighted MRI pre- (A) and post- (B) gadolinium. The posterior pituitary bright spot is absent on the noncontrast imaging. Following gadolinium administration, there is abnormal enhancement along the floor of the third ventricle (upper two arrows), together with widespread leptomeningeal enhancement (lower four arrows).
case_images: dgae565f2.jpg
case_images: PMC11747752_03_dgae565f2.jpg
case_images: dgae565-F2
case_images: Following gadolinium injection, abnormal enhancement was observed along the floor of the third ventricle and inferior to the optic chiasm with further leptomeningeal enhancement over the surface of the brainstem, cerebellum, and cervical cord (Fig. 2). Lack of a posterior pituitary bright spot (Fig. 2) is, however, not uniform in patients with AVP-D and may occur in PP: in a recent multicenter international study, the pituitary bright spot was absent in 68% of patients with AVP-D and in 14% of patients with PP, highlighting that MRI results need to be interpreted in the clinical context.