A Woman With Rheumatoid Arthritis Who Developed Numbness and Pain in the Feet

A 64-year-old woman with rheumatoid arthritis (RA) was being treated with oral prednisone, methotrexate 7.5 g weekly, and rofecoxib. She also received thyroid replacement, injections of Kineret (anakinra), a recombinant interleukin-1 receptor antagonist, and atenolol with hydrochlorothiazide for hypertension. She had a 4-month history of pain in the back of the thighs while sitting. This pain was so severe that she could not sit even for 10 minutes. An MRI of the thighs was normal.

Over the past 2 months, she developed tingling and numbness of the feet. She felt worse when she wore tight clothes or tennis shoes. She also had pain that shot down to the toes and numbness on the tips of her toes, mainly on the right side. The numbness had spread up to the middle right foot in the past month.

Past medical history included hysterectomy and chole cystectomy.

She did not smoke or drink. Family history was positive for RA in an aunt and two cousins. Her father died of amyotrophic lateral sclerosis.

Mentation and cranial nerves were unremarkable. There was no dryness of the mouth or conjunctiva. Some joint deformities were noticed. Strength and reflexes were normal, except for absent ankle jerks. There were no Babinski signs. Coordination and gait were normal. There were no Tinel’s signs in the tibial nerves at the ankles.

Sensory examination revealed mildly decreased vibration sense over the great toes and thumbs. Pinprick sensation was decreased in an asymmetric fashion: on the right foot, it was decreased up to the ankle, and on the left just decreased at the tips of her toes. The rest of the examination was unremarkable.

What is the Most Likely Diagnosis?

This patient with RA presented with burning feet. The possibility of tarsal tunnel syndrome needed to be considered. However, her sensory deficit included the dorsum of the feet and was up to the ankles, indicating a peripheral neuropathy that was asymmetric, suggesting a neuropathy from small vessel vasculitis associated with RA. This can also be seen in Sjögren syndrome, but she had no manifestation of this condition.

She also had hypothyroidism, which could cause a neuropathy, but was well maintained with thyroid supplement. In such cases other causes of a predominantly sensory neuropathy, such as diabetes, or B ₁₂ or other vitamin deficiencies, should also be considered. Secondary amyloidosis is rarely seen in patients with a known connective tissue disorder. She was not exposed to toxins or drugs and did not take an excessive amount of vitamins that could cause a neuropathy.

Her father had amyotrophic lateral sclerosis, but she had no symptoms or findings to suggest this disease, and her problem was typical of a neuropathy.

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	4.9	2	–
Fibular head	11.8	2	40
Knee	13.5	2	47

Tibial Nerve L.	Normal ≤ 5.3	Normal ≥ 4	Normal ≥ 40
Ankle	4.0	3	–
Pop. fossa	13.7	3	38

Ulnar Nerve R.	Normal ≤ 3.6	Normal ≥ 8	Normal ≥ 50
Wrist	2.8	11	–
Below elbow	6.0	10	56
Above elbow	12.0	10	60

F-Wave and Tibial H-Reflex Studies

Nerve	Latency (ms)	Normal Latency ≤ (ms)
Peroneal nerve R.	51.3	54
Tibial nerve L.	53.9	54
Ulnar nerve R.	29.7	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	3.9	4.0	9	11	40	40
Superficial peroneal nerve R.	3.2	3.5	3.7	4.0	5	8–10	44	40
Ulnar nerve R.	2.2	2.6	2.7	3.1	17	13	55	50

Sympathetic Skin Response

Hand R.—Normal

Foot R.—Absent

EMG Data

Muscle	Insrt Activity	Fibs	Pos Waves	Fasc	Amp	Dur	Poly	Pattern
Lumbar paraspinals R.	Norm	None	None	None	Norm	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.	Inc	None	1+	None	Norm	Norm	None	Full
Extensor hallucis longus R.	Inc	None	None	None	Norm	Norm	None	Full
Lumbar paraspinals L.	Norm	None	None	None	Norm	Norm	None	Full
Gastrocnemius L.	Inc	None	1+	None	Norm	Norm	None	Full
First dorsal interosseus L.	Norm	None	None	None	Norm	Norm	None	Full