Diagnosis and Treatment > Investigation > Serum osmolality

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Rayna Patel Department of Stroke Medicine, Addenbrooke’s Hospital, Cambridge, UK

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Waheed Mustafa Department of Orthopaedic Surgery, Basildon University Hospital, Nethermayne, Basildon, Essex, UK

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Michael T Sheaff Department of Pathology, St Bartholemew’s Hospital, London, UK

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Sami Khan Department of Radiology, Basildon University Hospital, Nethermayne, Basildon, Essex, UK

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Summary

IgG4-related disease (IgG4-RD) is a rare but increasingly recognised condition, emerging as a clinical entity following the observation of the associations of autoimmune pancreatitis. IgG4-RD is characterised by extensive infiltration of IgG4-positive plasma cells into multiple organs and raised serum IgG4 levels. Clinical manifestations of IgG4 disease classically include autoimmune pancreatitis, lacrimal or salivary gland infiltration (formerly known as Mikulicz disease) and retroperitoneal fibrosis. More rarely, IgG4 disease can cause pituitary hypophysitis. Although most frequently described in middle-aged males, the epidemiology and pathogenesis of the disease remain largely undefined. Nevertheless, an understanding of the wide variety of clinical manifestations of this multi-system condition is undeniably important given the often excellent outcomes following treatment. We describe an unusual presentation of IgG4 disease with isolated diabetes insipidus secondary to pituitary hypophysitis. The patient in question subsequently developed chest pain secondary to mediastinal lymphadenopathy and tubulo-interstitial nephritis leading to renal dysfunction. He was successfully treated with oral steroids and had regular follow-up, and remains well at follow-up 2 years later.

Learning points

  • IgG4 disease, although rare, is increasing in prevalence largely due to increased recognition of its clinical manifestations, including autoimmune pancreatitis, lacrimal or salivary gland infiltration, retroperitoneal fibrosis and, more rarely, lymphocytic hypophysitis presenting as diabetes insipidus.

  • IgG4 disease is highly treatable, and symptoms may show complete resolution with administration of steroids, highlighting the importance of correct and timely diagnosis.

  • Causes of lymphocytic hypophysitis are varied and not distinguishable radiologically. Given the difficulty in biopsying the pituitary, careful attention must be paid to the systemic clinical presentation to provide clues as to the underlying disorder.

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Michael Dick Faculty of Medical and Health Sciences, The University of Auckland, 85 Park Road, Grafton, Auckland, New Zealand

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Sarah R Catford Department of Endocrinology and Diabetes, The Alfred Hospital, Commercial Road, Melbourne, Victoria, 3004, Australia

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Kavita Kumareswaran Department of Endocrinology and Diabetes, The Alfred Hospital, Commercial Road, Melbourne, Victoria, 3004, Australia
Department of Medicine, Faculty of Medicine, Nursing and Health Sciences, Alfred Hospital, Monash University, Clayton, Victoria, 3168, Australia

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Peter Shane Hamblin Department of Endocrinology and Diabetes, The Alfred Hospital, Commercial Road, Melbourne, Victoria, 3004, Australia
Department of Medicine, Faculty of Medicine, Nursing and Health Sciences, Alfred Hospital, Monash University, Clayton, Victoria, 3168, Australia

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Duncan J Topliss Department of Endocrinology and Diabetes, The Alfred Hospital, Commercial Road, Melbourne, Victoria, 3004, Australia
Department of Medicine, Faculty of Medicine, Nursing and Health Sciences, Alfred Hospital, Monash University, Clayton, Victoria, 3168, Australia

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Summary

The syndrome of inappropriate antidiuretic hormone secretion (SIADH) can occur following traumatic brain injury (TBI), but is usually transient. There are very few case reports describing chronic SIADH and all resolved within 12 months, except for one case complicated by meningo-encephalitis. Persistent symptomatic hyponatremia due to chronic SIADH was present for 4 years following a TBI in a previously well 32-year-old man. Hyponatremia consistent with SIADH initially occurred in the immediate period following a high-speed motorbike accident in 2010. There were associated complications of post-traumatic amnesia and mild cognitive deficits. Normalization of serum sodium was achieved initially with fluid restriction. However, this was not sustained and he subsequently required a permanent 1.2 l restriction to maintain near normal sodium levels. Multiple episodes of acute symptomatic hyponatremia requiring hospitalization occurred over the following years when he repeatedly stopped the fluid restriction. Given the ongoing nature of his hyponatremia and difficulties complying with strict fluid restriction, demeclocycline was commenced in 2014. Normal sodium levels without fluid restriction have been maintained for 6 months since starting demeclocycline. This case illustrates an important long-term effect of TBI, the challenges of complying with permanent fluid restrictions and the potential role of demeclocycline in patients with chronic hyponatremia due to SIADH.

Learning points

  • Hyponatraemia due to SIADH commonly occurs after TBI, but is usually mild and transient.

  • Chronic hyponatraemia due to SIADH following TBI is a rare but important complication.

  • It likely results from damage to the pituitary stalk or posterior pituitary causing inappropriate non-osmotic hypersecretion of ADH.

  • First line management of SIADH is generally fluid restriction, but hypertonic saline may be required in severe cases. Adherence to long-term fluid restriction is challenging. Other options include oral urea, vasopressin receptor antagonists and demeclocycline.

  • While effective, oral urea is poorly tolerated and vasopressin receptor antagonists are currently not licensed for use in Australia or the USA beyond 30 days due to insufficient long-term safety data and specific concerns of hepatotoxicity.

  • Demeclocycline is an effective, well-tolerated and safe option for management of chronic hyponatraemia due to SIADH.

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Pedro Marques Endocrinology Department, Instituto Português de Oncologia de Lisboa, Francisco Gentil, Rua Professor Lima Basto1099-023, Lisboa, Portugal
Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford, UK

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Kavinga Gunawardana Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford, UK

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Ashley Grossman Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford, UK

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Summary

Gestational diabetes insipidus (DI) is a rare complication of pregnancy, usually developing in the third trimester and remitting spontaneously 4–6 weeks post-partum. It is mainly caused by excessive vasopressinase activity, an enzyme expressed by placental trophoblasts which metabolises arginine vasopressin (AVP). Its diagnosis is challenging, and the treatment requires desmopressin. A 38-year-old Chinese woman was referred in the 37th week of her first single-gestation due to polyuria, nocturia and polydipsia. She was known to have gestational diabetes mellitus diagnosed in the second trimester, well-controlled with diet. Her medical history was unremarkable. Physical examination demonstrated decreased skin turgor; her blood pressure was 102/63 mmHg, heart rate 78 beats/min and weight 53 kg (BMI 22.6 kg/m2). Laboratory data revealed low urine osmolality 89 mOsmol/kg (350–1000), serum osmolality 293 mOsmol/kg (278–295), serum sodium 144 mmol/l (135–145), potassium 4.1 mmol/l (3.5–5.0), urea 2.2 mmol/l (2.5–6.7), glucose 3.5 mmol/l and HbA1c 5.3%. Bilirubin, alanine transaminase, alkaline phosphatase and full blood count were normal. The patient was started on desmopressin with improvement in her symptoms, and normalisation of serum and urine osmolality (280 and 310 mOsmol/kg respectively). A fetus was delivered at the 39th week without major problems. After delivery, desmopressin was stopped and she had no further evidence of polyuria, polydipsia or nocturia. Her sodium, serum/urine osmolality at 12-weeks post-partum were normal. A pituitary magnetic resonance imaging (MRI) revealed the neurohypophyseal T1-bright spot situated ectopically, with a normal adenohypophysis and infundibulum. She remains clinically well, currently breastfeeding, and off all medication. This case illustrates some challenges in the diagnosis and management of transient gestational DI.

Learning points

  • Gestational DI is a rare complication of pregnancy occurring in two to four out of 100 000 pregnancies. It usually develops at the end of the second or third trimester of pregnancy and remits spontaneously 4–6 weeks after delivery.

  • Gestational DI occurrence is related to excessive vasopressinase activity, an enzyme expressed by placental trophoblasts during pregnancy, which metabolises AVP. Its activity is proportional to the placental weight, explaining the higher vasopressinase activity in third trimester or in multiple pregnancies.

  • Vasopressinase is metabolised by the liver, which most likely explains its higher concentrations in pregnant women with hepatic dysfunction, such acute fatty liver of pregnancy, HELLP syndrome, hepatitis and cirrhosis. Therefore, it is important to assess liver function in patients with gestational DI, and to be aware of the risk of DI in pregnant women with liver disease.

  • Serum and urine osmolality are essential for the diagnosis, but other tests such as serum sodium, glucose, urea, creatinine, liver function may be informative. The water deprivation test is normally not recommended during pregnancy because it may lead to significant dehydration, but a pituitary MRI should be performed at some point to exclude lesions in the hypothalamo-pituitary region.

  • These patients should be monitored for vital signs, fluid balance, body weight, fetal status, renal and liver function, and treated with desmopressin. The recommended doses are similar or slightly higher than those recommended for central DI in non-pregnant women, and should be titrated individually.

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N Atapattu Lady Ridgeway Hospital, Colombo, Sri Lanka

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K A C P Imalke General Hospital, Matara, Sri Lanka

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M Madarasinghe General Hospital, Matara, Sri Lanka

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A Lamahewage General Hospital, Matara, Sri Lanka

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K S H de Silva Lady Ridgeway Hospital, Colombo, Sri Lanka
Department of Paediatrics, Faculty of Medicine, University of Colombo, Colombo, Sri Lanka

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Summary

Children rarely present with phaeochromocytoma. Their presentation differs from that of adults. The classic triad of sweating, headache and palpitation may not always present in children with phaeochromocytoma. In this study, we present a 6-year-old girl who came to us with polyuria and polydipsia for evaluation of suspected diabetes insipidus. She gave a clear history of increased sweating in the recent past. On clinical examination, she was noted to have high blood pressure. Subsequent investigations revealed a phaeochromocytoma. Her polyuria and hypertension resolved immediately after the surgery. We did not have the facilities to arrange for genetic tests; however, the patient and the family members are under follow-up for other associated conditions.

Learning points

  • Polyuria and polydipsia are rare symptoms of phaeochromocytoma.

  • Complete physical examination prevented unnecessary investigations for polyuria and led to a correct diagnosis.

  • Classic features are not always necessary for diagnostic evaluation of rare diseases.

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Ramesh Srinivasan Department of Paediatric Endocrinology, Royal Victoria Infirmary, Newcastle-upon-Tyne Hospitals NHS Trust, Newcastle-upon-Tyne NE1 4LP, UK

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Stephen Ball Department of Endocrinology, Royal Victoria Infirmary, Newcastle-upon-Tyne NE1 4LP, UK
The Medical School, Newcastle University, Newcastle NE24HH, UK

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Martin Ward-Platt Ward 35, Royal Victoria Infirmary, Newcastle-upon-Tyne NE1 4LP, UK

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David Bourn The Institute of Genetic Medicine, Newcastle University, International Centre for Life, Central Parkway, Newcastle-upon-Tyne NE1 3BZ, UK

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Ciaron McAnulty The Institute of Genetic Medicine, Newcastle University, International Centre for Life, Central Parkway, Newcastle-upon-Tyne NE1 3BZ, UK

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Tim Cheetham Department of Paediatric Endocrinology, Royal Victoria Infirmary, Newcastle-upon-Tyne Hospitals NHS Trust, Newcastle-upon-Tyne NE1 4LP, UK
The Institute of Genetic Medicine, Newcastle University, International Centre for Life, Central Parkway, Newcastle-upon-Tyne NE1 3BZ, UK

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Summary

Aim: Differentiating familial cranial diabetes insipidus (CDI) from primary polydipsia can be difficult. We report the diagnostic utility of genetic testing as a means of confirming or excluding this diagnosis.

Patient and methods: The index case presented at 3 months with polydipsia. He was diagnosed with familial CDI based on a positive family history combined with what was considered to be suspicious symptomatology and biochemistry. He was treated with desmopressin (DDAVP) but re-presented at 5 months of age with hyponatraemia and the DDAVP was stopped. Gene sequencing of the vasopressin gene in father and his offspring was undertaken to establish the underlying molecular defect.

Results: Both father and daughter were found to have the pathogenic mutation c.242T>C (p.Leu81Pro) in exon 2 of the AVP gene consistent with a diagnosis of familial diabetes insipidus. The index case did not have the pathogenic mutation and the family could be reassured that he would not require intervention with DDAVP.

Conclusions: Gene sequencing of AVP gene can have a valuable role in predicting whether or not a child is at risk of developing CDI in future. This can help to prevent family uncertainty and unnecessary treatment with its associated risks.

Learning points

  • Differentiating patients with familial cranial diabetes insipidus from those with primary polydipsia is not always straightforward.

  • Molecular genetic analysis of the vasopressin gene is a valuable way of confirming or refuting a diagnosis of familial CDI in difficult cases and is a valuable way of identifying individuals who will develop CDI in later childhood. This information can be of great value to families.

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