Title: Endocrine / Pathology / Primary polydipsia anddiabetes insipidus

Q: Primary polydipsia and diabetes insipidus characterized by...?
A: the production of large amounts of dilute urine +/– thirst

Q: Urine specific gravity...?
A: < 1.006

Q: Urine osmolality usually...?
A: < 300 mOsm/kg

Q: When the Central DI may be transient ?
A: - If damage is below hypothalamic median eminence.
Or
- In the posterior pituitary.
(ADH in hypothalamus can still be secreted systemically via portal capillaries in median eminence).

Q: What is Primary polydipsia ?
A: Excessive water intake

Q: What are the causes of Primary polydipsia ?
A: - Psychiatric illnesses
- Hypothalamic lesions affecting thirst center

Q: Serum Osmolarity: [High or Low]
Primary polydipsia → [...]
Central DI → [...]
Nephrogenic DI → [...]
A: ↓; ↑; ↑

ADH level: [High or Low]
- Primary polydipsia → ↓ or normal
- Central DI → ↓
- Nephrogenic DI → Normal or ↑

Q: Water Restriction:
- [...] → Significant ↑ in urine osmolality (> 700 mOsm/kg)
- [...] → No change or slight ↑ in urine osmolality
- [...] → No change or slight ↑ in urine osmolality
A: Primary polydipsia; Central DI; Nephrogenic DI
Back Extra: **No water intake for 2–3 hours followed by hourly measurements of urine volume and osmolality as well as plasma Na+ concentration and osmolality.**

Q: Desmopressin Adminstration:
- [...] → —
- [...] → Significant ↑ in urine osmolality (> 50%)
- [...] → Minimal change in urine osmolality
A: Primary polydipsia; Central DI; Nephrogenic DI
Back Extra: **Desmopressin (ADH analog) is administered if serum osmolality > 295–300 mOsm/kg, plasma Na+ ≥ 145 mEq/L, or urine osmolality does not increase despite ↑ plasma osmolality.

Treatment:
- Primary polydipsia → Water restriction
- Central DI → Desmopressin (DDAVP)
- Nephrogenic DI → Manage the underlying cause; low-solute diet, HCTZ, amiloride, indomethacin