Case: 6-year-old Boy with Weakness

00:01 So let's start with a case.

00:03 A 6-year-old boy who presents with weakness.

00:06 This 6-year-old boy presents for new evaluation of weakness and difficulty walking.

00:11 The boy was born at 37 weeks by uncomplicated vaginal delivery.

00:15 He met all milestones well until about 3 years ago or 3 years of age, when he first started having difficulties with walking, particularly running longer distances, where he would get tired and weak.

00:29 Over the past several years, he has had progressive weakness with difficulty running, jumping and climbing.

00:35 He has no other medical conditions.

00:37 He's an only child and his mother is 42 years old, and has had an abnormal gait with arched back but no other signs of weakness.

00:46 And she does see a cardiologist for an unspecified heart rhythm abnormality.

00:53 Over the last 6 months, the boy's weakness has continued to worsen.

00:57 He now has difficulty standing up from a lying position.

01:00 His calf muscles are enlarged and hypertrophied bilaterally and symmetrically.

01:05 He has no problems breathing.

01:07 A neurologic examination shows proximal weakness in the arms and legs.

01:11 Cranial nerves, sensory examination, reflex exam and cerebellar exam are all normal.

01:18 Workup shows a markedly increased creatine kinase over 40,000 IU/mL.

01:25 So what's the most likely diagnosis? Well, let's go back and look through some of the key details of this case.

01:32 First, we see that this is a young child, which is tipping us off that this may be an inherited muscle disorder.

01:39 And the patient presents with progressive weakness, which is really important when we differentiate the muscular dystrophies from other inherited causes of muscle disorders.

01:49 On the second part of the case, we see a number of key findings.

01:53 First is the distribution.

01:55 This is proximal weakness, proximal in the legs and proximal in the arms.

01:59 And that really puts us into the bucket the category of proximal predominant muscular dystrophies.

02:06 What are the sensory findings? Well, here we see the sensory exam is normal.

02:10 The reflex exam is also normal.

02:12 And then there's a fourth important wildcard and that is calf muscle enlargement or hypertrophy or pseudohypertrophy, which will point us in the direction of a muscular dystrophy, that and we see this really elevated creatine kinase, which points us to some type of inflammation in and around the muscle.

02:31 So what's the most likely diagnosis? Polymyositis, Duchenne's muscular dystrophy, Limb-girdle muscular dystrophy or Dermatomyositis? Well, polymyositis is an acquired cause of muscle disorder and this patient presents with an age, a sex and a distribution of weakness that is not consistent, inconsistent with polymyositis.

02:54 Dermatomyositis presents with a rash in addition to acquired proximal muscle weakness, which is inconsistent with this case.

03:02 Limb-girdle muscular dystrophy can be seen as a cause of muscular dystrophy but this patient's age and sex really points us to Duchenne's muscular dystrophy.