A Man With Foot Pain

A 60-year-old man came with a 12-month history of shooting pains in the sole of the left foot along with numbness in the sole and occasional pain which radiated from the hip down. This was worse when he remained seated for a long time.

Previous workup included a normal MRI of the lumbosacral spine and an EMG, upon which he was diagnosed as having a tarsal tunnel syndrome (TTS). He was treated with steroid injections and then later received a nonsteroidal antiinflammatory drug and amitriptyline.

Past medical history was positive for coronary stent placement 5 years previously. Family history was positive for diabetes.

Examination revealed an obese man who had normal mental function and cranial nerves. Muscle strength was normal. Reflexes were equal and symmetrical. Sensory examination was normal. There was no Tinel’s sign in the retromalleolar area, but he had mild tenderness in the left hip. No mass was palpable, but this was hard to assess because of the patient’s size. Straight leg raising was negative. Back examination was normal.

What is the Differential Diagnosis?

This patient’s pain was indeed suggestive of TTS; however, the radiation to his hip might suggest an S1 radiculopathy or sciatic nerve lesion, particularly due to the tenderness in the hip. The diagnosis of TTS was made by EMG previously. His lumbosacral MRI done prior to referral was reviewed, and it was negative.

What is a Tarsal Tunnel Syndrome?

TTS is produced by compression of the tibial nerve at the ankle, causing shooting pains in the ankle and foot; later, patients might develop numbness in the sole of the foot and atrophy in the tibial-innervated foot muscles.

The diagnosis could be suggested by a positive Tinel’s sign in the retromalleolar area, but this is not always present. The differential diagnosis includes S1 radiculopathy, sciatic nerve lesions, other tibial nerve lesions, and a plantar neuropathy in the foot. Common causes of TTS are compression, neuromas, fibromas, fractures or other trauma, varicose veins, hypertrophy of the abductor hallucis muscle, lipoma, rheumatoid arthritis, and cysts.

The most useful diagnostic test for this patient was an EMG.

An EMG Test was Performed

Motor Nerve Studies

Nerve and Site	Latency(ms)	Amplitude (mV)	Conduction Velocity (m/s)
Peroneal Nerve L.	Normal ≤ 5.7	Normal ≥ 3	Normal ≥ 40
Ankle	5.1	5	–
Fibular head	12.8	4	42

Tibial Nerve L.	Normal ≤ 5.3	Normal ≥ 4	Normal ≥ 40
Ankle	4.2	15	–
Pop. fossa	14.8	8	43

Nerve and Site	Latency (ms)	Amplitude (mV)	Conduction Velocity (m/s)
Tibial Nerve L. (ADQP)	Normal ≤ 5.3	Normal ≥ 4	Normal ≥ 40
Ankle	5.9	7	–
Pop. fossa	16.4	3	41

F-Wave and Tibial H-Reflex Studies

Nerve	Latency (ms)	Normal Latency ≤ (ms)
Peroneal nerve L.	51.7	54
Tibial nerve L.	48.0	54
H-reflex L.	34.2	34
H-reflex R.	33.8	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 L.	3.5	3.5	4.0	4.0	15	11	40	40
Medial plantar L.	5.0	3.2	5.5	3.7	12	10	28	40
Lateral plantar L.	NR	3.2	NR	3.7	NR	8	NR	40
Medial plantar R.	3.1	3.2	3.6	3.7	13	10	45	40
Lateral plantar R.	3.2	3.2	3.7	3.7	8	8	44	40