Muscular weakness is not unusual with PN. Muscle biopsies done in areas where there is neuropathy are often quite abnormal. Muscle biopsies done farther away from neuropathic regions (usually the stocking and glove areas) are generally normal unless some other condition is going on.

Many hereditary myopathies are associated with neuropathies... You can have neurogenic myopathies.

You can get sarcopenia from aging, or disuse....sarcopenia is like osteopenia...one is bone (osteo) one is muscle (sarco).

People with PN generally do respond to exercise. A combination of aerobic and resistance training, stretching and balance work it best.

I think a lot of PTs are discouraged these days as it used to be a great profession to go into and now insurances have limited benefits....they seldom get to see improvements in their patients except in the most motivated of the bunch.

If you have a heritable neuropathy, the approaches are different, as those generally come with more arthropathy....altho any PN will disrupt proprioception in joints and cause joint deformity and can cause gait abnormalities which can result in fractures, ulcers or just plain deformity.

Sensory nerves give and take positional input to the tendons and ligaments...and motor neurons move muscles...you generally don't have neuropathy without some muscle involvement....the amount of and location of that involvement Proximal or Distal or both depends on the kind of neuropathy you have, or if you a comorbid myopathic condition.

There are some myopathies that do not respond to exercise, but in general, a consistent exercise program will result in gains in strength and improvement of affect.

BTW, muscle biopsies are invasive and generally not done unless there is a suspected myopathy (muscle disease). It is surgical and causes substantial swelling...and yes, they hurt.....they are not done in neuropathic areas, such as in stocking and glove distributions as that is where they will be abnormal due to the neuropathy....they are done in areas where they feel the neuropathy would not produce muscle abnormality....if abnormal there, usually additional pathology is going on.