A Young Man With Large and Stiff Muscles

An 18-year-old patient had complained of muscle stiffness since he was 2½ years old, impairing his ability to exercise. He felt less stiff after warming up, and cold made the symptoms worse. His past medical history was unremarkable, and a review of systems was negative. He denied weakness or other neurologic symptoms. Family history revealed that his mother had muscle stiffness with a well-developed musculature all her life.

On examination he had normal mentation and cranial nerves, except for delayed relaxation of the orbicularis oculi muscles after forceful contraction. He was well built with prominent muscles ( Fig. 107-1 ) but had no weakness. There was delayed relaxation after a muscle contraction from gripping or percussion. Reflexes, coordination sensory tests, and the rest of the examination were normal.

What is the Most Likely Diagnosis?

The differential diagnosis of muscle enlargement includes hereditary myopathies, such as Becker’s dystrophy, and some limb-girdle dystrophies, myotonia congenita, amyloidosis, hypothyroidism, stiff-person syndrome, and parasitic infection, among others ( Table 107-1 ). Myotonic dystrophy sometimes presents initially without prominent weakness or atrophy, but those patients do not have muscle hypertrophy. Schwartz–Jampel syndrome manifests with muscle hypertrophy and myotonia, but the patient did not have the short stature or skeletal anomalies seen in this disease. The family history and early onset are against an acquired disorder of muscle irritability such as Isaacs syndrome. He had no activity-exacerbated myotonia to suggest paramyotonia congenita.

Table 107-1

Neuromuscular Causes of Muscle Hypertrophy

Adapted from Griggs R, Mendell JR, Miller RG, eds. Evaluation of the patient with myopathy. In: Evaluation and Treatment of Myopathies . Contemporary Neurology Series. Philadelphia, PA: FA Davis; 1995:26.

Generalized hypertrophy

Juvenile spinal muscular atrophy (usually early, mainly calves)

Postpolio pseudohypertrophy

Acromegaly

Hypothyroid myopathy

Schwartz–Jampel syndrome

Isaacs syndrome

Myotonia congenita

Paramyotonia congenita

Duchenne muscular dystrophy (can be generalized but mainly in the calves)

Becker muscular dystrophy

Limb-girdle muscular dystrophy (mainly in the calves, but could be generalized in some)

Flier syndrome

Sarcoidosis (can be focal)

Parasites (cysticercosis, schistosomiasis, and trichinosis)

Amyloidosis

Focal hypertrophy

Sarcoidosis

Radiculopathy of other causes of partial denervation (e.g., tethered cord)

Tendon rupture

The most likely consideration in this case with hereditary muscle hypertrophy and myotonia is myotonia congenita, Thomsen type.

An EMG Test was Performed

Motor Nerve Studies

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Median Nerve R.	Normal ≤ 4.2	Normal ≥ 6	Normal ≥ 50
Wrist	3.2	15	–
Elbow	6.7	15	59

Peroneal Nerve R.	Normal ≤ 5.7	Normal ≥ 3	Normal ≥ 40
Ankle	4.7	8	–
Fibular head	12.7	7	42
Knee	14.1	7	46

F-Wave Studies

Nerve	Latency (ms)	Normal Latency ≤ (ms)
Median nerve R.	27.8	30
Peroneal nerve R.	48.0	54

Sensory Nerve Studies

Nerve	Onset Latency (ms)	Normal Onset Latency ≤ (ms)	Peak Latency (ms)	Normal Peak Latency ≤ (ms)	Amp (μV)	Normal Amp ≥ (μV)	Conduction Velocity (m/s)	Normal Conduction Velocity ≥ (m/s)
Median nerve R.	2.3	2.6	2.8	3.1	35	20	57	50
Sural nerve R.	3.1	3.5	3.6	4.0	20	11	45	40

EMG Data

Muscle	Insrt Activity	Fibs	Pos Waves	Fasc	Amp	Dur	Poly	Pattern
Deltoid R.	Myot	None	None	None	Norm	Norm	None	Full
Biceps brachii R.	Myot	None	None	None	Norm	Norm	None	Full
Flexor carpi radialis R.	Myot	None	None	None	Norm	Norm	None	Full
Extensor digitorum com. R.	Myot	None	None	None	Norm	Norm	None	Full
First dorsal interosseous R.	Myot	None	None	None	Norm	Norm	None	Full
Vastus lateralis R.	Myot	None	None	None	Norm	Norm	None	Full
Tibialis anterior R.	Myot	None	None	None	Norm	Norm	None	Full
Gastrocnemius R.	Myot	None	None	None	Norm	Norm	None	Full