A 50-year-old man complains of slowly progressive weakness over several months. Walking has become more difficult, as has using his hands. There are no sensory, bowel, or bladder complaints; he denies problems with thinking, speech, or vision. Examination shows distal muscle weakness with muscle wasting and fasciculations. There are also upper motor neuron signs, including extensor plantar reflexes and hyperreflexia in wasted muscle groups.
Which of the following tests is most likely to be abnormal in this patient?
A. Cerebrospinal fluid white blood cell countThe disease described involves motor neurons exclusively. Amyotrophic lateral sclerosis affects both upper and lower motor neurons. In this patient, there is upper and lower motor neuron involvement without sensory deficit. Lower motor neuron signs include focal weakness, focal wasting, and fasciculations. Upper motor neuron signs include an extensor plantar response and an increased tendon reflex in a weakened muscle. Peripheral neuropathy and dementia do not occur in ALS. Muscular dystrophy, polymyositis, and the neuromuscular junction disorder myasthenia gravis cause (usually proximal) muscle weakness but not the atrophy and upper motor neuron signs seen in this patient. EMG in the patient with ALS shows widespread denervation and fibrillation potentials with preserved nerve conduction velocities. Sensory testing is normal. There is no inflammatory reaction in the CSF. CT or MRI of the brain may be necessary to rule out a mass in the region of the foramen magnum. In most patients, a CT of the cervical spine is necessary to rule out a structural lesion of the spine, which could mimic ALS. Thyroid studies and vitamin B12 levels may be useful in peripheral neuropathy but not in motor neuron disease.