Neurology Patient B


History

The following is a patient described in Hospital Practice, October 15, 1997, p.111.

Patient's Comments

Patient B is a 19 year old man who reported left leg weakness and numbness. He was working on a fishing boat in the Gulf of Alaska when he fell over backwards agains a wall on his buttocks. He experienced an immediate shocklike sensation down his left leg from his waist to his foot. He also experienced numbness and tingling, which resolved within minutes. Within several hours he returned to his deck work.

The next morning, he awoke with left leg numbness from the knee to the foot and weakness of the left ankle in the form of a footdrop. The symptoms worsened over several weeks and then resolved. Since he was at sea, he did not seek medical attention, but he changed his activity to accommodate his disability. He was left with a mild but persistent numbness of the left leg below the knee and a left footdrop. He had no symptoms in any other limbs.

Doctor's Comments

The medical history did not uncover any neurologic abnormalities and the family history likewise was unremarkable. He was not taking any medications.

Physical examination showed normal function of the cranial nerves. Upper extremity motor and sensory function were also normal. Examination of the legs showed normal muscle tone. (But careful examination nonetheless revealed abnormalities.) The left calf was 2 cm smaller than the right. Manual muscle testing of the proximal muscles revealed normal strength on the right but grade 4+ weakness on the left. (A higher number indicates a greater deficit.) Ankle dorsiflexion was weak bilaterally, grade 4+ on the left and grade 3 on the right. Measures of distal strength, such as toe flexion and extension, were normal on the right but grade 3+ to 4 on the left. Tendon reflexes were present but reduced in the arms and at the knees and absent at the ankles bilaterally. Sensory examination was remarkable only for a mildly decreased perception of light touch over the dorsum of the left foot and up part of the leg.

The patient brought a copy of a magnetic resonance imaging (MRI) scan of the spine that had been performed at another institution. The scan showed mild disk bulging, but no herniation or bony abnormality that could account for the degree of dysfunction, and certainly not its bilateral distribution.



QUESTION: What is consistent here with a contusion pressing on a nerve and thus causing the symptoms?

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QUESTION: But what makes you suspicious that more is involved?

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QUESTION: What next information would be helpful?

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Tests and Diagnosis

A nerve condition study and EMG showed that sural responses were absent bilaterally.

Peroneal motor responses were markedly reduced bilaterally, with slowed conduction velocities. There apparently was a bilateral block across the fibular head.

The tibial motor response was of normal amplitude, but the conduction velocity was slow.

Sensory responses in the arms were of low amplitude and motor responses in the ulnar nerve showed slowing across the elbow.

The EMG study showed bilateral evidence of chronic denervation of mild degree....

Lumbar puncture showed no abnormalities in the cerebrospinal fluid.

Genetic testing finally revealed that the patient had a genetic demyelinating disorder. He was missing one copy of the gene coding for a protein found in myelin. This is similar to Charcot-Marie-Tooth disease, although in this example the demyelination mainly tends to occur when pressure is applied to the nerve. If a piece of a small nerve is removed and examined histologically, the myelin is grossly abnormal in appearance.

Treatment

The patient was advised to refrain from physically traumatic vocations and avocations.