When muscle mass is affected, in a person who exercises...
one has to wonder about damage to the axons.

Sensory neuropathies sometimes do not spread to include
the axons. When axons are affected, it suggests an autoimmune event (including reactions to vaccines), a toxin, or
a hereditary neuropathy which is inescapable.

Because something was "checked" does not mean it was interpreted correctly. A level of 250 for B12 in the US will not
be flagged for a doctor to notice. And many do not even know about the new 400pg/ml level that is 10 yrs old now.

Many doctors miss this. That is why I am here.

There can be antibodies to the myelin coat of the axons. Or as Marlene has stated, the cell itself is attacked, and mitochondria damaged. Mitochondria provide the energy for the cell to live and do its job.

A skin biopsy can show if you have sensory loss of neurons and is quite benign compared to that old sural biopsy.

Since you drink often, you could try Thiamine B1 300mg daily in divided doses, or its improved form Benfotiamine 300mg daily (don't need to divide the dose), for 3 months and see if there is any change. Thiamine is a cofactor in the metabolism of alcohol, and when low, or used up, the aldehydes may accumulate and damage nerves. Both of these are OTC.
Thiamine in most drug stores, inexpensive. Benfotiamine is mostly online. I use Doctor's Best, as it is a quality company and affordable. iherb.com and Amazon and some other discount online suppliers have it now.