Which spinal nerve root is most likely affected in a patient with weak wrist extension and paresthesias in the thumb and index finger?

The most likely spinal nerve root affected in a patient with weak wrist extension and paresthesias in the thumb and index finger is indeed the cervical 6 root. This nerve root contributes to the innervation of the muscles responsible for wrist extension, primarily through the radial nerve, which is derived from the C5 and C6 nerve roots.

In this scenario, weakness in wrist extension suggests potential impairment of the musculature innervated by the radial nerve, indicating a compromise at the level of cervical 6. Additionally, the presence of paresthesias specifically in the thumb and index finger correlates strongly with the sensory distribution supplied by this nerve root.

Cervical 4 and cervical 5 do not primarily influence wrist extension; instead, cervical 4 is typically associated with shoulder function and sensation in the shoulder area, while cervical 5 contributes mainly to shoulder abduction and some elbow flexion. Cervical 7 may involve wrist extension but often presents with symptoms affecting more of the middle finger and is less likely to produce specific symptoms in the thumb and index finger alone. Therefore, cervical 6 stands out as the most relevant root in this clinical presentation, as it cohesively links the observed weakness and sensory changes.