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Polyuria in a patient with fibrosing alveolitis

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Causes of neurogenic diabetes insipidus

  • idiopathic: familial (autosomal dominant inheritance)

  • malignancy: primary (eg, craniopharyngioma), metastatic (eg, lung, breast)

  • granuloma: eg, sarcoid, histiocytosis

  • infection: eg, meningitis, encephalitis

  • traumatic: accidental, surgical

  • vascular: eg, vasculitis

  • toxic: carbon monoxide

  • congenital malformations

A 70-year-old Caucasian male smoker, with known cryptogenic fibrosing alveolitis, was admitted with increasing dyspnoea and a 3-month history of thirst, polyuria and polydipsia. Cryptogenic fibrosing alveolitis had been diagnosed 9 years previously on clinical and physiological criteria, and by chest radiograph abnormalities (figure 1). There was no history of asbestos exposure. He had initially responded to oral steroids, but over the previous 2 years there had been a gradual objective and subjective deterioration in his clinical state and lung function, despite frequent trials on high-dose steroids. On admission he was dyspnoeic at rest and had a productive cough. He complained of unquenchable thirst, marked polyuria and polydipsia. He had a poor appetite but his weight was stable. Treatment included prednisolone 7.5 mg od, captopril 12.5 mg bid (for hypertension), salbutamol inhaler and 2 litres of oxygen on a prn basis.

On examination he was cyanosed and clubbed. Chest auscultation revealed bilateral fine crepitations. There was no clinical evidence of cardiac impairment. Central nervous system examination, including fundoscopy and visual field, was normal. Initial investigations revealed: haemoglobin 11.6 g/dl, white cell count 13.8 × 109/l , platelets 527 × 109/l, erythrocyte sedimentation rate 29 mm/h, Na 144 mmol/l, K 3.9 mmol/l, bicarbonate 29 mmol/l, chloride 103 mmol/l, urea 5 mmol/l, calcium 2.32 mmol/l and blood glucose 6.2 mmol/l. Arterial blood gasses on 28% inspired oxygen revealed pO2 of 10.3 kPa and pCO2 of 3.3 kPa. Liver function tests, thyroid function tests, early morning cortisol, angiotensin-converting enzyme and prolactin levels were normal. His total 24-hour water intake and urine output were 6600 ml and 6150 ml, respectively. Urine and serum osmolarity were 158 mmol/l and 300 mmol/l, respectively.

Questions

1
What does the chest X-ray show?
2
What two specific investigations are indicated?
3
How would you interpret the results?
4
What specific treatment is indicated?

Answers

QUESTION 1

There is mediastinal shift to the right and extensive basal reticulo-nodular shadowing, predominantly in the right lower zone. (Serial reviews of the chest X-rays over 2 years showed no significant change.)

QUESTION 2

Water deprivation test (table) and magnetic resonance imaging (MRI) of the head (figures 2 and3).

QUESTION 3

In normal subjects, following water deprivation test, the urine osmolarity increases to approximately 800 mmol/l and serum osmolarity to between 280–300 mmol/l. If plasma osmolarity is greater than 295 mmol/l and serum sodium is greater than 143 mmol/l, then primary or psychogenic polydypsia is excluded. After injection of desmopressin, if the urine osmolarity rises more than 50% above the value at the end of the deprivation test, then neurogenic diabetes insipidus is established.1 The results in our patient (table) were consistent with a diagnosis of neurogenic diabetes insipidus.

Table Water deprivation test. At 16.30, the patient received an injection of 2 mg desmopressin

MRI shows an enhancing mass invading the pituitary gland with extension up the stalk into the hypothalamus (figure 2). In figure 3, there is a small enhancing deposit in the left hemisphere of the cerebellum. These findings are consistent with metastatic carcinomatosis.

QUESTION 4

Treatment of neurogenic diabetes insipidus requires vasopressin administration. The preparation of choice is desmopressin (DDAVP), a long-acting synthetic vasopressin analogue given intranasally at a dose of 5–10 μg once or twice a day. There is no specific treatment for metastatic carcinomatosis of unknown primary.

Outcome

Prostatic-specific antigen and abdominal ultrasound were normal. He was too breathless to undergo fibre-optic bronchoscopy. He continued to deteriorate with increasing dyspnoea, haemoptysis and bilateral pedal oedema. A ventilation and perfusion lung scan showed possible multiple pulmonary emboli, but despite heparinisation, he became increasingly hypoxic and died. At autopsy there was evidence of congestive cardiac failure, macroscopic fibrosing alveolitis (honey comb lung) and lung carcinoma of the right lower lobe with metastases to the hypothalamus, spleen and vertebral column. Histology showed an adenocarcinoma. There was no evidence of pulmonary emboli.

Discussion

Metastases in the pituitary region are infrequently encountered and are only usually observed late in the clinical presentation of cancer or at autopsy.2 3 Series of neurogenic diabetes insipidus suggest that 8.2% of cases are due to metastatic carcinoma.4 The most common sites of the primary tumour are the breast (50%), lung (20%), gastrointestinal tract (6%), prostrate (6%), melanoma (2%), and other primary sites (16%).5

Although lung tumours, and especially small cell carcinoma, give rise to cerebrospinal metastases in 10–30% of patients, only sporadic cases of neurogenic diabetes insipidus due to pituitary and hypothalamic involvement have been reported.6 Even less common is the presentation of diabetes insipidus as the first manifestation of lung cancer.7 Almost one in 10 patients with cryptogenic fibrosing alveolitis develops lung cancer. There is an excess relative risk of 14.1 compared to a general population of comparable age, sex and smoking habits.8Granulomatous diseases, such as sarcoidosis and histiocytosis, should be considered in the differential diagnosis of interstitial lung disease and neurogenic diabetes insipidus.

Final diagnosis

Neurogenic diabetes insipidus due to metastatic carcinomatosis.

References

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