Guillain-Barré Syndrome (GBS): Although the classic presentation of GBS includes ascending paralysis, the absence of dysautonomia and cranial nerve involvement does not rule it out entirely. The rapid progression and subsequent improvement are consistent with GBS, especially in an elderly patient.

Acute Myelitis: This condition, often due to an inflammatory or infectious process affecting the spinal cord, can present with rapid onset of limb weakness. The lack of dysautonomia and cranial nerve involvement could still fit within the spectrum of acute myelitis, depending on the level and extent of spinal cord involvement.
Acute Demyelinating Neuropathy: Similar to GBS but with a focus on demyelination, this condition can present with rapid progression of weakness without the necessity of cranial nerve or autonomic involvement.

Spinal Cord Infarction: Although less common, a spinal cord infarction can present with rapid onset of limb weakness. Given the potential for severe and permanent disability, missing this diagnosis could be catastrophic.
Spinal Epidural Hematoma or Abscess: These conditions are medical emergencies that can present with rapid progression of neurological deficits, including limb weakness. Prompt diagnosis and intervention are critical to prevent permanent damage.

Neuromuscular Junction Disorders (e.g., Myasthenia Gravis, Botulism): While these conditions can cause rapid progression of weakness, they are less likely given the specific pattern of limb involvement and the absence of characteristic features such as fluctuating weakness or specific cranial nerve findings.
Toxic or Metabolic Causes: Certain toxins or metabolic derangements can cause rapid onset of weakness. These would be rare but should be considered, especially if there's an exposure history or systemic symptoms suggestive of a metabolic disorder.