We previously reported 2 patients who developed profound sensory loss following treatment with high doses of parenteral pyridozine (vitamin Bg).1 These patients lost their ability to perceive joint posi tion, vibration, light touch, and well-localized pain. One year after the initial insult, neither patient had recovered sensory function; motor function, including swallowing and speech, was impaired because of the Bensory deficits. The underlying pathology probablywas identical to the degeneration of dorsal root and trigeminal ganglia neurons documented in animal models ofpyridozine intoxication.27 In addi tion to absent sensory responses, we found sequential electrodiagnostic evidence of mild motor nerve or neuron involvement, most consistent with a distal to proximal axonal atrophy from disuse. We report clinical and electrodiagnostic findings in 1 ofthese patients 4>/z years after her initial illness. Case report. This 32-year-old woman (case 1 in the previous report) reported no recovery of lost sensation. With the exception of head position, she denied any capacity to determine the location of her extremities in space with her eyes closed. Similarly, she reported insensitivity to touch, loss of tactile perception, and inability to localize pain. Poorly localized deep pain sensation was preserved and she reported heightened sensitivity to noxious stimuli. She is unable to stand or walk, and requires a wheelchair for mobility. Transfers are possible only with direct visual observation of her limbs. Any motor activity, including rolling over in bed, is impossible in total darkness. Her speech, formerly dysarthric, has returned to normal. She gave the intriguing history oflearningto speak normally by listening to herself. She requires a pureed diet because she is unable to perceive objects in her mouth or pharynx and is at risk for aspiration of a solid piece of food. Neurologic examination disclosed normal mental status. Visual fields were normal to confrontation. Extraocular movements, includ ing pursuit, convergence, and saccadic eye movements were normal. Examination of facial sensation revealed absent cutaneous, mucosal, and corneal light touch sensation. Pin-pain was perceptible but not localizable. Gag reflex was weak. The remainder ofthe cranial nerves were normal. Upper-extremity strength was normal. In the lower extremities, proximal strength was normal with mild (4+/5, MRC scale) and symmetric distal weakness consistent with disuse. Rapid movements were slowed; finger to nose and heel-knee-shin manuevers were well performed under direct visualization. With eyes closed, there were athetotic movements ofthe fingers and toes, and her arms drifted aimlessly in space. Position sense was absent in all extremities except for gross neck movements. Light touch, pin-pain, and vibratory sensations were absent. Poorly localized deep pain sensa tion was present with a diminished threshold ofpain. She was able to stand only with assistance, and ambulation was impossible. Muscle stretch reflexes were absent and plantar responses were flexor. Electrophysiologic data. Median, ulnar, and sural nerve sensory nerve action potentials were absent. Median and ulnar compound muscle action potential (CMAP) amplitude, distal latency, and con duction velocity were normal. Peroneal CMAP amplitude was bor derline-low with normal distal latency and conduction velocity. All F responses were normal. Needle examination of the right biceps brachii and left anterior tibialis muscles were normal except for irregular motor unit recruitment, particularly when making move ments with the eyes dosed. Discussion. The sensory abnormalities produced by acute pyridoxine intoxication are permanent and profound. Despite exten sive rehabilitation, this woman remains severely disabled by her sensory neuropathy-neuronopathy. In contrast, the mild motor ab normalities detected by previous electrophyBiologic studies have dis appeared. We speculated previously that some of the motor abnormalities found by electrodiagnostic studies were due to disuse. This hypothesis is less tenable given the normalization of motor electrophysiologic findings during continued limb disuse. Acute highdose pyridoxine intoxication in humans mayproduce mild, reversible motor nerve or neuron dysfunction. The permanence of the sensory deficits is unusual but consistent with a neuronopathy, and emphasizes the danger of administering high doses of pyridoxine.
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Jun 12, 2021
Monica Alcantara + 5
Open Access
