Darren Abaya, a 4-year old male, was brought into the clinic by his parents because
of his shortness of breath and weakness in his arms and legs. On initial examination, Darren appeared only mildly fatigued. His mother reported he had been crawling around the waiting room
playing aggressively with the train set. According to past medical records, Darren
achieved his gross motor skill milestones (e.g., holding head up, sitting, rolling, &
standing) on pace with other children. However, he didn’t begin walking until 17
months.
Darren is 35 pounds and 2’2” and his vital signs are:
heart rate = 108 beats per minute (normal = 60 – 100 beats per minute)
respiratory rate = 25 breaths per minute (normal range = 12 – 20 breaths per minute)
In the physical exam, pupils were normal and reactive to light. Mother notes that development of speech was slightly delayed. No facial muscle weakness was noted. Breath sounds were reduced and cough was very weak. Heart sounds were normal (no murmur). Shoulder, arm, and thigh
muscles appear slightly atrophied, but calf muscles appeared slightly enlarged.
Muscle strength reduced in the biceps brachii & triceps brachii muscles (+3 on a scale from 0 to
+5, +5 being normal)
In the examination with Darren, the parents also reported the following:
Mother: “It is so hard for us to tell what he is really feeling. Sometimes I just think he is having
growing pains. But what really started to worry us is when he started getting short of breath
about a week ago and just had no energy to climb at the playground like normal.”
Father: “We took him to the playground and tried to play a game of tag. Darren would get just a few
steps in and plop down heaving. We also noticed that he started to stop to take a break when he
was going up the stairs to his bedroom in our home. He just seems to always be breathing harder than usual.”
Questions:
1. Describe the difference between skeletal, cardiac, and smooth muscles. Which of these muscle tissues do you think are involved in Darren’s disease or condition?
2. What are the six major functions of the muscular system? Which of these functions are problematic for Darren?
4. Thinking about how a muscle contracts - what are some possible reasons a muscle would fail to
contract? Explain at least one.
5. Why might Darren be experiencing muscle weakness? What disease or condition do you think Darren suffers from and why?
