Disorders of Vasopressin - Tutorial Flashcards
48F - mother of 2, presenting with polyuria, nocturia and polydipsia What would be your differential diagnosis?
Diabetes Mellitus (DM) Diabetes Insipidus (DI) Psychogenic polydipsia (PP) Anxiety - disruption of sleep
Thinking about your differential diagnosis, what tests could the GP do next?
The standard is to do blood and urine tests to look at BGL and Na+ Urine test - look for glucose in the urine, look at urine concentration To diagnose DM - could use Hb1ac (but 3 months half life, affected by pregnancy), could use BGL: Fasting of over 7, or more than 11.1 randomly Blood test - look at plasma BGL, plasma osmolality, look for plasma Na+ levels Refer to hospital for water deprivation test
Fasting plasma glucose 5.4mmol/L HbA1c 36 mmol/mol (<42 mmol/mol) Serum sodium 148 mmol/L (135-145 mmol/L) How do these results help you with the differential diagnosis?
Rule out DM - BGL normal High plasma Na+ levels = likely to be DI and not PP as that would result in low plasma Na+ levels
Work through the water deprivation test results. What would be the response to water deprivation in a healthy person? How does that compare to the test results here?
During a water deprivation test = measure vol + conc. of all urine passed. Intermittent blood tests to look at plasma osmolality
In an healthy individual: the plasma osmolality would stay in a similar range, the urine volume would decrease over time, and the urine concentration would increase over time
In comparison to 45F, her urine volume stays similar throughout, her urine osmolality increases very little, and her plasma osmolality increases
She hasn’t lost too much weight
Why do we monitor weight during the water deprivation test?
To monitor dehydration - if they loose 3% of their body weight, stop test
What is the diagnosis?
She has DI - she cannot concentrate her urine, even when deprived of water
CDI (cranial diabetes insidipus) - after ddAVP (synthetic vasopressin) was given, her urine volume decreases and her urine concentration increases. Ability to respond to ddAVP = CDI
How should this patient be treated?
How is dosage determined?
Given desmopressin nasal spray or as a tablet
Dosage determined by reduction in symptoms, not using vasopressin reference range
What are the pros and cons of desmopressin in nasal spray Vs tablet form?
Typically nasal spray gets confused with hay fever / allery nasal sprays and so are often missed out on charts
Peptide hormones = difficult to deliver via tablets due to stomach acid. Absorption = variable with ddAVP tablet
Nasal spray = ddAVP into circulation straight away, absorption = more consistent and better
