An Elderly Man With New Onset Weakness

A 70-year-old male with hypertension, hyperlipidemia with a past medical history of chronic migraine, chronic lower back pain and coronary artery disease, and S/P triple bypass was referred for progressive proximal extremity weakness over the past 6 months. The weakness started with both lower extremities and later involved the upper extremities and neck, not associated with myalgia.

The patient was on atorvastatin, which was stopped, but the weakness did not improve. He denied dysarthria, dyspnea, dysphagia, worsening lower back pain, numbness, cramps, and fasciculations.

On physical examination he was noted to have normal cognition on screening. Cranial nerve examination revealed left cranial nerve VI palsy (secondary to prior ischemic cranial nerve VI); otherwise, cranial nerve exam was unremarkable. On motor exam there was moderate weakness appreciated in the deltoids, hip flexors, quadriceps, and hamstrings. Deep tendon reflexes were 2+ and symmetrical bilaterally. Sensory examination revealed minimal decreased vibration sensation in the toes. Coordination was intact. The patient had difficulty walking with an unsteady gait.

Serum CK was 2612 IU/L (normal, <200 IU/L), aspartate aminotransferase (AST) was 54 IU/L, and ALT 85 IU/L, and the rest of the lab tests were within normal limits including normal thyroid stimulating hormone (TSH), T3, T4, HIV, and ANA. Myositis panel was negative, which included anti-5-nucleotidase, cytosolic IA (NT5C1A), anticysolic 5-nucleotidase 1A (CN1A) antibody, anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibody. HIV was negative.

An EMG Test was Performed

Motor Nerve Conduction

Nerve and Site	Latency (ms)	Amplitude (mV)	Segment	Latency Difference (ms)	Conduction Velocity
Peroneal nerve L.
Ankle	4.8	10.1	Extensor digitorum brevis–ankle	4.8
Fibula (head)	10.8	9.6	Ankle–fibula (head)	6.0	50 m/s
Popliteal fossa	12.5	9.9	Fibula (head)–popliteal fossa	1.7	53 m/s
Tibial nerve L.
Ankle	5.1	9.6	Abductor–hallucis–ankle	5.1	m/s
Popliteal fossa	14.0	5.9	Ankle–popliteal fossa	8.9	51 m/s
Tibial nerve R.
Ankle	5.0	13.4	Abductor–hallucis–ankle	5.0	m/s
Popliteal fossa	14.4	4.6	Ankle–popliteal fossa	9.4	44 m/s
Peroneal nerve R.
Ankle	5.1	6.6	Extensor digitorum brevis–ankle	5.1	m/s
Fibula (head)	11.0	6.0	Ankle–fibula (head)	5.9	51 m/s
Popliteal fossa	12.4	6.0	Fibula (head)–popliteal fossa	1.4	64 m/s

F-Wave Studies

Nerve	M-Latency	F-Latency
Peroneal nerve L.	12.5	46.9
Tibial nerve L.	14.0	49.5
Tibial nerve R.	5.0	51.7
Peroneal nerve R.	13.1	51.5

Sensory Nerve Conduction

Nerve and Site	Onset Latency (ms)	Peak Latency (ms)	Amplitude (μV)	Segment	Latency Difference (ms)	Conduction Velocity
Sural nerve L.
Lower leg	2.8	3.6	26	Ankle–lower leg	2.8	m/s
Superficial peroneal nerve L.
Ankle	2.5	3.2	16	Dorsum of foot–ankle	2.5	m/s
Superficial peroneal nerve R.
Ankle	2.4	3.4	19	Dorsum of foot–ankle	2.4	m/s
Sural nerve R.
Lower leg	2.7	3.4	17	Ankle–lower leg	2.7	m/s