A Boy With Short Stature, Small Jaw, Muscle Hypertrophy, and Stiffness
A 5-year-old boy was seen for muscle stiffness. He was the product of a normal pregnancy of a 27-year-old woman and had normal developmental milestones until he developed progressive limb spasms and difficulty opening and closing his mouth at age 2 years. He had marked muscle hypertrophy and short stature; he was treated with carbamazepine, which produced some improvement of the spasms. The patient had one healthy brother and two healthy sisters. Family history was otherwise negative.
Physical examination revealed a boy with short stature for his age at 92 cm, which is below the limits of normal for his age (normal, 100 cm) ( Fig. 109-1 ), and a very small jaw, low-set ears, and prominent eyebrows. Neurologic examination was normal except for marked muscle hypertrophy, muscle stiffness, and percussion myotonia. The rest of the examination was unremarkable.
Fig. 109-1
Patient showing very prominent muscles. He had a small chin. The face is not shown at parent’s request.
What is the Differential Diagnosis?
The differential diagnosis of this patient with prominent muscles and stiffness is rather limited. It includes hypothyroidism, but the myotonia is against this diagnosis. Myotonia congenita is another consideration. The patient’s facial deformities and prominent eyebrows, micrognathia, and short stature are consistent with Schwartz–Jampel syndrome.
An EMG Test was Performed
Motor Nerve Conduction
Nerve and Site
Latency (ms)
Amplitude (mV)
Conduction Velocity (m/s)
Ulnar Nerve R.
Normal ≤ 3.6
Normal ≥ 8
Normal ≥ 50
Wrist
2.4
13
–
Below elbow
4.8
13
63
Above elbow
6.8
12
60
Peroneal Nerve R.
Normal ≤ 5.7
Normal ≥ 3
Normal ≥ 40
Ankle
2.3
6
–
Fibular head
5.5
6
53
Knee
7.5
6
50
F-Wave Studies
Nerve
Latency (ms)
Normal Latency ≤ (ms)
Ulnar nerve R.
23.1
30
Peroneal nerve R.
41.0
54
Sensory Nerve Studies
Nerve
Onset Latency (ms)
Normal Onset Latency ≤ (ms)
Amp (μV)
Normal Amp ≥ (μV)
Ulnar nerve R.
2.6
3.1
18
13
Sural nerve R.
3.2
4.0
20
11
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