Upper motor neuron dysfunction causes limb spasticity, hyperreflexia (including Babinski's sign and a brisk jaw-jerk reflex), and emotional lability. Lower motor neuron dysfunction causes limb muscle weakness, atrophy, cramps, and fasiculations, as well as dysarthria, dysphagia, and difficulty in mastication. At the time of initial presentation, extremity cramping, fatigue, and weakness are seen, as well as muscle fasciculations and atrophy. 5 These symptoms are more prominent in the upper extremities, with asymmetric weakness seen commonly. Regardless of the initial symptomatology, widespread motor and respiratory dysfunction progresses within weeks to months. Atrophic, fasciculating, hyperreflexic extremities are seen, as well as foot drop and claw deformity of the hand. Patients also may present with an atrophic fasciculating tongue and monotonous speech, with relative sparing of facial and eye movements. Patients with fALS more often present with isolated lower extremity weakness and atrophy at the time of diagnosis. Some patients eventually diagnosed as having ALS present initially with cervical or back pain consistent with an acute compressive radiculopathy, leading to surgery. Despite successful operative intervention, these patients develop significant muscle wasting consistent with motor neuron dysfunction shortly after the procedure.6
Progressive respiratory muscle weakness causes dyspnea with mild activity, until dyspnea at rest occurs. Dementia and parkinsonism also may be seen in up to 15 percent of patients, especially those with fALS. Other cognitive problems such as apathy, poor attention and motivation, and altered social skills may be noted in patient with ALS.
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