A Woman With Long-standing Weakness and Foot Deformities

A 43-year-old woman had had progressive leg weakness for 6 years, but she stated that she had been mildly weak since childhood when she had several falls. She had always walked on her tiptoes and was diagnosed as having “tight heel cords.” She was told then that she might have some form of muscular dystrophy.

The patient was the product of a normal delivery; she was not floppy, sat at 8 months, spoke at 10 months, and started walking at the age of 2 years. Her mother and maternal grandfather had similar problems. Past medical history included polycystic kidney disease.

Examination revealed normal mentation and cranial nerves. There was no muscle atrophy. She had difficulty arising from a chair ( Fig. 87-1A ). Manual muscle testing revealed strength in neck flexors 4+/5 and shoulder abduction of 4+/5; biceps, triceps, and forearm muscles were 5/5 hip flexors, extensors, and thigh muscles were 4/5; and foot dorsiflexors were 4−/5. Reflexes were normal in the arms and only trace at the knees and ankles. Sensation to touch, vibration, and pinprick were normal. Coordination was normal. There were no Babinski signs or fasciculations. She had contractures of the Achilles tendons and small feet with mildly high arches (see Fig. 87-1B ). The examination was otherwise unremarkable.

What is the Differential Diagnosis?

This woman had weakness and high arches mainly in the legs and depressed reflexes suggesting a hereditary neuropathy; however, there was no other clinical suggestion of a neuropathy, and the weakness was more proximal. She could also have had spinal muscular atrophy, but the lack of fasciculations and normal reflexes was against that diagnosis. The lack of fluctuation and cranial nerve involvement was against a disorder of neuromuscular transmission.

She appeared to have a myopathy, and those considered in the differential diagnosis were congenital myopathies of slow progression, such as central core disease (CCD) and some cases with congenital-fiber-type disproportion. Most other congenital myopathies are more progressive and severe, although cases of rod or nemaline myopathy may start later (adult-onset rod myopathy). A limb-girdle muscular dystrophy or a manifest carrier state of a dystrophinopathy are also considerations; an endocrine myopathy and polymyositis seem very unlikely as the weakness was long-lasting and she had a positive family history. Other possibilities include acid maltase and carnitine deficiencies, but the apparent pattern in inheritance is not autosomal-recessive as in those disorders. A mitochondrial myopathy and proximal myotonic myopathy (PROMM) are also considerations. The lack of myotonia is against the latter diagnosis, but this may not be clinically obvious at times.

The family history, which suggests an autosomal-dominant inheritance, narrows the differential diagnosis to either CCD or limb-girdle dystrophy type I (LGMD 1) and, less likely, PROMM.

What Tests Should be Done?

Complete metabolic panel and thyroid-stimulating hormone were normal. Serum creatine kinase was mildly elevated up to 260 IU/L (normal, <200 IU/L).

An EMG Test was Performed

Motor Nerve Studies

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Peroneal Nerve R.	Normal ≤ 5.7	Normal ≥ 3	Normal ≥ 40
Ankle	4.5	4	–
Fibular head	10.4	3	46
Knee	11.8	3	58

F-Wave and Tibial H-Reflex Studies

Nerve	Latency (ms)	Normal Latency ≤ (ms)
Peroneal nerve R.	44.0	54
H-reflex R.	28.6	34

Sensory Nerve Study

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)
Sural nerve R.	3.0	3.5	3.5	4.0	17	11	47	40

EMG Data

Muscle	Insrt Activity	Fibs	Pos Waves	Fasc	Amp	Dur	Poly	Pattern
Lumbar paraspinals R.	Norm	None	None	None	Norm	Norm	None	Full
Deltoid R.	Norm	None	None	None	Dec	Brief	Many	Full ^a
Iliopsoas R.	Norm	None	None	None	Dec	Brief	Many	Full
Tensor fasciae latae R.	Norm	None	None	None	Dec	Brief	Few	Full ^a
Vastus lateralis R.	Norm	None	None	None	Dec	Brief	Few	Full ^a
Tibialis anterior R.	Norm	None	None	None	Dec	Brief	Few	Full
Gastrocnemius R.	Norm	None	None	None	Norm	Norm	None	Full