A Man With Pheochromocytoma and Back Pain

A 46-year-old male was referred for evaluation because of intense low back pain and tingling in the anterior aspect of the right thigh for about 3 weeks’ duration.

He was diagnosed to have pheochromocytoma 3½ years earlier. At that time he presented with an abdominal mass which was resected, but he did not have systemic manifestations of pheochromocytoma, as the tumor was nonfunctional. He received chemotherapy for 2 years. Past medical history was otherwise unremarkable.

Family history was noncontributory except for a sister who had Hodgkin disease.

General physical examination was unremarkable except for mild tenderness on palpation of the back. Cranial nerves were normal. Strength and reflexes were normal, except for the right knee and adductor reflexes which were trace. There was decreased sensation to light touch and pinprick over the anterior aspect of the right thigh.

What is the Differential Diagnosis?

The distribution of symptoms and findings suggests a disorder affecting nerve roots L2–L4, particularly because of the decreased knee and adductor reflexes on the right and decreased sensation in the anterior aspect of the thigh.

The possibility that this is produced by tumor invasion to the spine is an important consideration. The differential diagnosis includes a disk herniation.

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	5.5	3	–
Fibular head	13.0	3	43

Tibial Nerve R.	Normal ≤ 5.3	Normal ≥ 4	Normal ≥ 40
Ankle	4.5	20	–
Pop. fossa	14.7	16	42

F-Wave and Tibial H-Reflex Studies

Nerve	Latency (ms)	Normal Latency ≤ (ms)
Peroneal nerve R.	54.0	54
Tibial nerve R.	52.5	54
H-reflex R.	29.1	34
H-reflex L.	29.0	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.	3.4	3.5	3.9	4.0	22	13	41	40

EMG Data

Muscle	Insrt Activity	Fibs	Pos Waves	Fasc	Amp	Dur	Poly	Pattern
Lumbar paraspinals R.	Inc	None	2+	None	Norm	Norm	None	Full
Iliopsoas R.	CRDs	None	None	None	None	Norm	None	Full
Vastus lateralis R.	Norm	None	None	None	Norm	Norm	None	Full
Adductor longus R.	Inc	1+	1+	None	Norm	Norm	None	Full
Adductor magnus R.	Inc	None	None	None	Norm	Norm	None	Full
Gracilis R.	Inc	1+	1+	None	Norm	Norm	None	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