An Older Woman With Leg Weakness and Atrophic Muscle Fibers on Biopsy

A 72-year-old woman presented with a 1-year history of lower extremity weakness and pain with difficulty going upstairs. She denied numbness or tingling paresthesias.

Previous workup by the referring neurologist included an EMG that showed “mild peripheral neuropathy” with many polyphasic motor unit action potentials. A muscle biopsy showed only mild type II muscle fiber smallness.

Past medical history was significant for gout, which was well controlled with allopurinol. She did not smoke or drink.

Examination revealed normal mentation and cranial nerves. She could not rise from a chair without using her hands, could not sit on a stool without assistance, and had difficulty sitting from a supine position, but gait was normal. Manual muscle testing revealed mild weakness only of the hip flexor abductors and extensors. Reflexes were normal without delayed relaxation of the ankle reflex or myoedema. Sensory and cerebellar examinations were normal. She had no pathologic reflexes.

What is the Differential Diagnosis?

The differential diagnosis in an older person with slowly progressive lower extremity weakness and pain includes peripheral neuropathy secondary to diabetes or several other causes such as pernicious anemia, toxins, and an alcoholic or paraneoplastic neuropathy. She did not have the characteristic glove-and-stocking sensory loss associated with a neuropathy. Spinal stenosis causes weakness with leg and back pain. The lack of dry mouth, pupillary abnormalities, and normal reflexes is against Eaton–Lambert syndrome.

The lower extremity proximal weakness could be from an inflammatory myopathy such as polymyositis or inclusion body myositis (IBM). The lack of neck flexor or proximal arm weakness was against polymyositis; the lack of significant quadriceps and distal muscle involvement was against IBM, and her muscle biopsy apparently ruled out both possibilities. The possibility of a late-onset muscular dystrophy was not supported by the biopsy. Endocrine myopathies such as hypothyroidism (see Case 87) and hyperparathyroidism can cause predominant leg weakness, and the muscle biopsy may show type II muscle fiber atrophy. Polymyalgia rheumatica, in addition to disuse atrophy due to muscle pain, should be considered, but polymyalgia rheumatica does not cause weakness.

What Other Tests Should be Done?

Blood chemistry profile was normal, except for glucose of 115 mg/dL (normal, 74–113 mg/dL), blood urea nitrogen, 21 mg/dL (normal, 5–20 mg/dL), calcium, 11.4 mg/dL (normal, 8.6–10.4 mg/dL), and alkaline phosphatase, 197 IU/L (normal, 39–134 IU/L). Thyroxine and thyroid-stimulating hormone were normal. Erythrocyte sedimentation rate was normal. Glycosylated hemoglobin was 6.26 g/dL (normal, 4.40–6.40 g/dL). Serum creatine kinase (CK) was 150 IU/L (normal, 50–200 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	3.7	3	–
Fibular head	10.3	3	51
Knee	11.7	3	52
Before exercise	–	3	–
Posttetanic	–	3	–

Tibial Nerve L.	Normal ≤ 5.3	Normal ≥ 4	Normal ≥ 40
Ankle	4.7	4	–
Pop. fossa	12.7	3	51

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Ulnar Nerve R.	Normal ≤ 3.6	Normal ≥ 8	Normal ≥ 50
Wrist	2.9	15	–
Elbow	6.7	14	61

F-Wave and Tibial H-Reflex Studies

Nerve	Latency (ms)	Normal Latency ≤ (ms)
Peroneal nerve R.	53.5	54
Tibial nerve L.	53.0	54
Ulnar nerve R.	29.9	30
H-reflex R.	34.0	34
H-reflex L.	34.0	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.	3.1	3.5	3.6	4.0	13	11	45	40
Superficial peroneal nerve R.	2.8	3.5	3.3	4.0	12	8–10	50	40
Ulnar nerve R.	2.5	2.6	3.0	3.1	15	13	50	50

EMG Data

Muscle	Insrt Activity	Fibs	Pos Waves	Fasc	Amp	Dur	Poly	Pattern
Deltoid R.	Norm	None	None	None	Dec	Brief	Few	Full
Biceps brachii R.	Norm	None	None	None	Norm	Norm	None	Full
Brachioradialis R.	Norm	None	None	None	Norm	Norm	None	Full
Flexor carpi radialis R.	Norm	None	None	None	Norm	Norm	None	Full
Flexor carpi ulnaris R.	Norm	None	None	None	Norm	Norm	None	Full
First dorsal interosseous R.	Norm	None	None	None	Norm	Norm	None	Full
Tensor fasciae latae R.	Norm	None	None	None	Norm	Norm	Few	Full
Vastus lateralis R.	Norm	None	None	None	Norm	Norm	Few	Full
Tibialis anterior R.	Norm	None	None	None	Norm	Norm	None	Full
Peroneus longus R.	Norm	None	None	None	Norm	Norm	None	Full
Gastrocnemius R.	Norm	None	None	None	Norm	Norm	None	Full