A Man With Muscle Pains

A 55-year-old man was referred for evaluation of muscle pains at rest, mainly in the thighs and calves and occasionally in the arms, and an elevated serum creatine kinase (CK). The muscle pains were present for 8 months, while the patient was on atorvastatin calcium for hyperlipidemia but persisted when the medication was discontinued. He denied weakness.

Past medical history was unremarkable. He did not smoke or drink. Family history was negative for neurologic disorders.

Examination revealed normal mentation and cranial nerves. There was normal muscle bulk and muscle strength. Reflexes were normal, and there were no pathologic reflexes. No myotonia, myoedema, or fasciculations were detected. Sensation, coordination, and gait were normal. There were no skin lesions, and the examination was otherwise unremarkable.

What is the Differential Diagnosis?

Hypothyroidism is an important consideration in patients with hyperlipidemia and muscle pains. It is unlikely that atorvastatin was the cause of his symptoms as they persisted after discontinuation of the drug.

Metabolic myopathies usually cause pain during or after exercise.

An inflammatory myopathy is also a possibility as such patients have muscle pains and elevated serum CK, but they usually also have muscle weakness. Fasciitis and polymyalgia rheumatica could cause muscle pains, but in these the CK levels are usually normal.

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	5.3	9	–
Fibular head	12.2	8	45
Knee	14.2	8	48

Ulnar Nerve R.	Normal ≤ 3.6	Normal ≥ 8	Normal ≥ 50
Wrist	3.1	8	–
Below elbow	7.1	8	54
Above elbow	9.4	8	55

F-Wave and Tibial H-Reflex Studies

Nerve	Latency (ms)	Normal Latency ≤ (ms)
Peroneal nerve R.	51.1	54
Ulnar nerve R.	29.7	30
H-reflex R.	30.2	34
H-reflex L.	31.6	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.	3.4	3.5	3.9	4.0	16	11	41	40
Superficial peroneal nerve R.	3.2	3.5	3.7	4.0	19	8–10	44	40
Ulnar nerve R.	2.2	2.6	2.7	3.1	17	13	55	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	Norm	Brief	Few	Full ^a
Extensor digitorum com. R.	Norm	None	None	None	Norm	Brief	Few	Full ^a
First dorsal interosseous R.	Norm	None	None	None	Norm	Norm	None	Full
Vastus lateralis R.	Norm	None	None	None	Norm	Brief	Few	Full ^a
Tibialis anterior R.	Norm	None	None	None	Norm	Brief	Few	Full
Gastrocnemius R.	Norm	None	None	None	Norm	Norm	None	Full