SIADH: Clinical Presentation

00:00 Now, before I go on though, I want to make sure we are clear about one thing.

00:05 “Dr. Raj, we didn’t talk about nephrogenic diabetes insipidus.” Oh yes, we did.

00:10 We did that in nephrology.

00:12 So, if you want your full explanation and discussion of nephrogenic diabetes insipidus, please refer to nephrology where there, we-we referred to the receptors not working properly.

00:24 And so, therefore, you will also will have polyuria and polydipsia.

00:30 But, in that case, you would then have ADH levels being quite high because their receptors are resistant.

00:40 Here we have SIADH.

00:42 Your patient with SIADH, who is he or she? Well, if there’s SIADH, maybe perhaps that surgery that I keep referring to, the transphenoidal, there’s every possibility that you might be releasing too much ADH from the posterior pituitary.

00:59 Keep that in mind.

01:01 Or there might be drugs such as Carbamazepine in which it may then result in increased release of ADH or you could be paraneoplastic.

01:12 For example, a lung cancer that you should know of known as small cell lung cancer, huh, may result in increased release of ADH.

01:22 Welcome to syndrome of inappropriate anti-diuretic hormone.

01:27 Most will then appear as being asymptomatic, that’s important, and here, because you’re diluting your plasma, you are going to then result in hyponatremia.

01:36 So, before we move on with SIADH, whatever the cause may be, here the plasma osmolality will be low and urine osmolality will be incredibly high.

01:46 You’re going to be forming concentrated urine, aren’t you? Now, what’s also important is the following.

01:52 Even though you’re reabsorbing this water… reabsorbing this water… reabsorbing this water, this comes back to our definition of transudate and exudate.

02:01 Symptoms - severe hyponatremia thus lethargic, seizures and coma.

02:07 Now, hyper or hyponatremia, you will have CNS issues.

02:13 Usually seen with acute reductions in serum sodium.

02:20 Seen as disorders with SIADH.

02:22 Causes.

02:23 Now, keep in mind, trauma, we saw both with diabetes… central diabetes insipidus and SAIDH.

02:34 Comes back to that point, if you destroy that posterior pituitary, there’s every possibility that here, you might be releasing too much ADH.

02:41 And in the end, you might completely deplete your posterior pituitary resulting in what, please? Good, central diabetes insipidus.

02:51 If you are unfamiliar with that spectrum prior, make sure that it is perfectly clear now.

02:56 With that said, take a look – stroke, trauma, haemorrhage, infection, psychosis.

03:02 What phase? The second phase.

03:04 The first and second phase are the triphasic event during that neurosurgery.

03:08 I’m not going to go through this one more time, I’ve talked about this plenty.

03:13 Thoracic disease, this is a big one.

03:16 You find many a surgeons, in which especially thoracic surgeons, when they’re performing this whatever procedure for thoracic surgery that the patient may present with SIADH.

03:30 Pneumonia, HIV patients with pneumocystis… bacterial, viral, TB; pneumonia may often present with SIADH.

03:39 I want you to put together pneumonia and thoracic disease together and whenever there is either surgery/invasive or pneumonia/infection, your patient may present with SIADH.

03:53 There are theories out there, but for the most part, you remember even the lung with cancer with small cell may result with SIADH.

04:00 So, different things in the thoracic region often associated with SIADH.

04:08 Drugs result in SIADH.

04:11 SSRIs, chlorpropramide, carbamezapine, high-dose IV cyclophosphamide.

04:13 SSRIs, chlorpromazine, carbamezapine, high-dose IV cyclophosphamide.

04:18 It’s a list that you want to make sure that you memorize before taking your boards.

04:24 Other causes of SIADH.

04:29 Hereditary gain of function mutation.

04:32 Alright, so, we’ll take a look at this.

04:34 Here, it behaves like SIADH.

04:37 You can have loss of function or gain of function.

04:41 If it’s loss of function, before we move on, take a look at the receptors that we have here, arginine vasopressin V2 receptors, arginine vasopressin V2 receptors.

04:53 Where are these receptors located? Good, kidney.

04:59 If it’s loss of function of the receptors, what’s your diagnosis? Nephrogenic diabetes insipidus.

05:08 If it’s gain of function, it behaves like SIADH; urine here is going to be concentrated.

05:17 These are type of questions that you’re going to get on your boards, absolute thinking questions.

05:24 How common is this? Not very common, but what, do the boards love this? Oh yeah, they do because it’s asking you about gain and loss of function, completely changing your presentation and diagnosis of your patient.

05:37 Here’s ectopic ADH, where? Thoracic.

05:43 What cancer? Lung.

05:46 What kind? Small cell lung cancer, a type of bronchogenic lung cancer.