This patient should receive riluzole. Clinical and electromyographic evidence of simultaneous upper and lower motoneuron signs in multiple body regions is most consistent with a diagnosis of amyotrophic lateral sclerosis (ALS). Onset in a single limb, rapid progression, bulbar involvement, and MRI evidence of a corticospinal tract abnormality are other findings that support a diagnosis of ALS, which can be confirmed by results of a needle electrode examination. The absence of an alternative likely cause of his symptoms, such as Lyme disease, hyperparathyroidism, vitamin B₁₂ or copper deficiency, lead intoxication, or combined cervical myelopathy and neuropathy, also suggests the diagnosis.

Riluzole is an FDA-approved medication for ALS and can increase the survival of affected patients by a modest average of 3 months. It can be offered to all patients with a new diagnosis of ALS who wish to maximize their survival. Edaravone is another option recently approved by the FDA for ALS; in one study, patients with early-stage ALS taking this medication had less of a decline in daily functioning, as measured by clinical assessment, than did those receiving placebo over a 24-week period.

Bilevel positive airway pressure and other similarly noninvasive respiratory support methods can increase survival in ALS and should be started in the presence of respiratory symptoms and hypercarbia, which are absent in this patient.

Although intravenous immune globulin (IVIG) can be used in the management of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), this patient's clinical history and findings on needle electrode examination, especially the prominent upper motoneuron signs and absence of sensory deficits, are inconsistent with CIDP. IVIG is not indicated for the management of ALS.

Percutaneous endoscopic gastrostomy should be considered in patients with ALS and dysphagia before they reach the advanced stages of the disease to improve nutrition and increase survival. This intervention would be premature in this patient, however, who has no signs of dysphagia.