The inability to produce concentrated urine due to either antidiuretic hormone deficiency or resistance, which leads to extreme thirst and polyuria. The diagnosis may be confirmed using a water deprivation test.
To diagnose diabetes insipidus, a detailed and full general examination is mandatory in the initial assessment. The respiratory system should be examined in detail for signs of sarcoidosis, tuberculosis and other connective tissue diseases.
A postural drop in BP indicates intravascular volume depletion. Skin turgor and mucous membranes should also be assessed.
Signs of Wegener's granulomatosis should be sought.
This should be performed in all patients due to the possibility of metastatic disease or germ cell tumours.
The thyroid gland should be examined in all patients presenting with possible metastatic disease.
The joints should be examined in detail for signs of connective tissue disease.
Muscle wasting may occur in glucocorticoid deficiency.
Proximal myopathy may occur in hypokalaemia or hypothyroidism and slow relaxing reflexes may occur with loss of thyroid function.
Consider performing this in all patients presenting with apparently isolated DI in case of metastatic disease.
Full assessment of acuity and fields is mandatory in all patients suspected of DI to detect chiasmal compression or other involvement of the optic pathways.
Disc pallor is indicative of long-term visual loss which may not recover after decompression of the optic pathway.
Papilloedema is an indicator of raised intracranial pressure requiring urgent investigation.
Full cranial nerve assessment is important in all patients with suspected peri-pituitary tumours.
The nerves of the cavernous sinus are most frequently affected, though a VI nerve palsy may be a false localising sign associated with increased intracranial pressure.
Turgor is assessed by pinching the skin of the back of the hand and observing how quickly the skin resumes its usual character.
Fine wrinkling of the skin occurs in hypopituitarism.
Pallor may also occur with a normocytic normochromic anaemia with glucocorticoid deficiency.
Doughy pallid 'myxoedematous' skin may be seen with loss of thyroid function.
Specifically seek signs of thyroid dysfunction.