An Elderly Woman With Proximal Weakness

A 76-year-old woman presented with a 6-month history of progressive weakness in the arms and legs.

Past medical history was positive for hypertension, hypothyroidism, and a left mastectomy for localized cancer 10 years previously. She was on sertraline HCl, diltiazem HCl, and thyroid replacement.

Family history was noncontributory. She did not smoke or drink.

She complained of a crawling sensation in her leg muscles periodically and noticed that her fingernails were not growing. She also was losing weight.

Previous EMG done elsewhere revealed a “mild demyelinating neuropathy.”

Mentation and cranial nerve examination were unremarkable. The pupils were equal and reactive, and the disks were flat. The tongue was not atrophic, dry, or weak. She had mild weakness in the proximal muscles with some fatigue, although at times this had a “giveaway” characteristic. There was no improvement after repetitive motion. She had difficulty rising up from a chair, could not sit up from a supine position, and was not able to walk on her tiptoes or squat. Reflexes were trace in the upper extremities and knees, and absent in the ankles. These did not change with repetitive testing. There were no Babinski signs. She had decreased vibration sense in the toes, but pinprick was normal. No atrophy or fasciculations were noted. Coordination was normal.

What is the Differential Diagnosis?

This patient had a history of proximal muscle weakness and had evidence of a mild peripheral neuropathy clinically and by her previous EMG. An acquired demyelinating neuropathy such as chronic inflammatory demyelinating polyneuropathy is a consideration. Her proximal weakness could also be secondary to hypothyroidism or hyperparathyroidism. Other possibilities include polymyositis, and, particularly because of her age, inclusion body myositis, but the distribution of weakness is against the latter. The lack of fasciculations is against progressive spinal muscular atrophy. This and hyporeflexia are against amyotrophic lateral sclerosis. Another possibility would be a disorder of neuromuscular transmission. She had no ptosis or bulbar muscular weakness, and the decreased reflexes are against myasthenia gravis but could suggest Lambert–Eaton syndrome. She, however, had no history of fatigue or improvement after a short period of muscle activity, nor did she have dry mouth or abnormal pupils to suggest this syndrome.

Complete blood count, serum creatine kinase and metabolic panel, T4, thyroid-stimulating hormone, B ₁₂ /folate, and acetylcholine receptor antibodies were normal. Antinuclear antibody titer was greater than 1:320; C-reactive protein and complements were normal.

An EMG Test was Performed

Motor Nerve Studies

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Ulnar Nerve R.	Normal ≤ 3.6	Normal ≥ 8	Normal ≥ 50
Wrist	3.5	2.3	–
Below elbow	10.7	2.4	37

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Peroneal Nerve R.	Normal ≤ 5.7	Normal ≥ 3	Normal ≥ 40
Ankle	5.5	2	–
Fibular head	12.6	1	40

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Tibial Nerve L.	Normal ≤ 5.3	Normal ≥ 4	Normal ≥ 40
Ankle	3.7	4	–
Pop. fossa	12.8	4	42

F-Wave and H-Reflex Studies

Nerve	Latency (ms)	Normal Latency ≤ (ms)
Peroneal nerve R.	54.3	54
Tibial nerve L.	55.2	54
Ulnar nerve R.	30.0	30
H-reflex R.	NR	34
H-reflex L.	NR	34

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)
Sural nerve R.	3.5	3.5	4.0	4.0	6	11	40	40
Ulnar nerve R.	2.5	2.6	3.0	3.1	12	13	50	50

EMG Data

Muscle	Insrt Activity	Fibs	Pos Waves	Fasc	Amp	Dur	Poly	Pattern
Deltoid R.	Norm	None	None	None	Norm	Norm	None	Full
Biceps brachii R.	Norm	None	None	None	Variable	Norm	None	Red
Flexor carpi ulnaris R.	Norm	None	None	None	Norm	Norm	None	Full
First dorsal interosseous R.	Norm	None	None	None	Variable	Norm	None	Full
Vastus lateralis R.	Norm	None	None	None	Norm	Norm	None	Full
Tibialis anterior R.	Norm	None	None	None	Norm	Norm	None	Full
Gastrocnemius R.	Norm	None	None	None	Norm	Norm	None	Full
Tibialis anterior L.	Norm	None	None	None	Norm	Norm	None	Full
Gastrocnemius L.	Norm	None	None	None	Norm	Norm	None	Full