Case: 42-year-old Man with Weakness

00:01 In this lecture, we're going to learn about Neoplastic or Paraneoplastic causes of neuromuscular junction disorders.

00:08 We're going to focus on Lambert-Eaton myasthenic syndrome.

00:12 A really rare but fascinating syndrome that you know it when you see it and say you ought to know it so you can see it.

00:20 Let's start with a case.

00:21 This is a 42-year-old man who presents with weakness.

00:25 This 42-year-old man presents for evaluation of weakness and new right upper lobe lung mass.

00:32 He reports three months of blurry vision, sometimes double vision, as well as weakness that began in his arms and have progressed to include his legs.

00:42 He's been unable to ride his motorcycle due to these symptoms.

00:45 He reports a 20-pound weight loss in the last three months.

00:49 He has no fatigable weakness but does report dry mouth, that is also new.

00:54 Examination shows bilateral ptosis, mild dysarthria, proximal upper and lower extremity weakness, normal sensation, and diffuse hyporeflexia.

01:06 So, what's the diagnosis? Well, let's look at those three main features of a peripheral nervous system disorder.

01:13 What's the distribution? What are the sensory findings? What's the reflex exam? And are there any important wildcard symptoms present in this case? The distribution here, involves bulbar weakness.

01:26 We see bilateral ptosis, mild dysarthria, there are bulbar findings, in addition to proximal weakness.

01:33 That's the distribution that doesn't support a muscle localization.

01:37 This doesn't sound like peripheral nerve dermatome.

01:40 This sounds like a neuromuscular junction disorder, proximal weakness with prominent bulbar findings.

01:47 The sensory exam is normal pointing away from a nerve problem and the reflexes show hyporeflexia.

01:53 Not a reflexia likely would see with a nerve problem, but diffuse hyporeflexia that is supportive of a junctional disorder.

02:01 What about wildcard features? Well, here this patient has a right upper lobe lung mass, that's concerning.

02:07 It needs to be further evaluated and a 20-pound weight loss.

02:10 We're worrying about cancer and a possible cancer associated condition like a paraneoplastic disorder.

02:17 Let's look at this patient's chest x-ray.

02:20 We see that here.

02:21 We see the normal findings of the lung and the heart, and this opacity in the right lung, that's concerning for a new mass and needs to be further evaluated in this for a possible lung cancer.

02:35 So what's the diagnosis? Is this myasthenia gravis, organophosphate poisoning, botulism toxicity or Lambert-Eaton myasthenic syndrome? All our neuromuscular junction disorders, all can present with weakness.

02:48 Which one is present in this case? Well, myasthenia gravis could be the case for this patient.

02:56 But with a new lung mass, a 20-pound weight loss, we have to be concerned for an alternative etiology.

03:02 The patient has not ingested organophosphates, and organophosphate poisoning does not sound like, the likely diagnosis for this patient.

03:09 There's no exposure to botulism toxin to suggest botulism or botulism toxin toxicity.

03:16 This is a case of Lambert-Eaton myasthenic syndrome.

03:19 And we see a classic presentation of proximal weakness with prominent bulbar fibers, excuse me, prominent bulbar findings and some other important clinical features that point us in that direction.

03:30 Lambert-Eaton is associated with certain types of cancer and we're concerned that this patient may have a new diagnosis of lung cancer.