Both you and Steve are correct, Liza Jane--there are predominantly small-fiber neuropathies, and these are by definiton axonal, and there are axonal neuropathies that affect primarily the larger myelinated fibers. There are also people with mixed types, as demonstrable on EMG/NCV and skin biopsy.

The distinctions may lie primarily in the causes--discovered and suspected. Many researchers feel, for example, that many of the "idiopathic" small-fiber neuropathies--those not caused by impaired glucose tolerance prior to diabetes or some other cause many non-specialists don't know to look for, like celiac/gluten sensitivity or unusual vasculitic conditions (I wonder about Alan as regards the latter)--may in the end be due to autoimmune mechanisms yet to be discovered. If one subscribes to the autoimmune molecular mimicry hypothesis, in which the body fights off a pathogen, but that pathogen has a structure similar enough to some structure of individual nerve for the attack to continue on those nerves, whether small axons, large axons, or both are attacked depend on the pathogen and one's own individual biochemical nerve structure. In fact, Dr. Latov and crew believe that it may get VERY specific. There are subtle differences in biochemical structure among types of an individual's small fiber nerves, for example--the C-axons, the A-alpha axons, the A-delta axons--and this may lead to a preferential attack on one group or other, with corresponding symptom differences (pain vs. numbness vs. temperature disruption). Add to that Dr. Moghekar's contention that one can also get preferential attacks on fibers at the dorsal root ganglia that are autoimmune in nature, leading to NON-length dependent conditions more accurately termed neuronopathies (they've always suspected this with me--it tends to produce body-wide, rather than progressive length dependent die back), and one can see how complicated this gets.

Dr. Latov believes that autoantibodies that attack certain parts of small-fiber axons will eventually be identified, just as a number of autoantibodies of larger nerve and of myelin (anti-MAG, anti-GM, anti-GQ, etc.) have been "discovered" over the last two decades.

And, of course, neuropathies that involve circulatory compromise, such as are found in diabetes and in many vasculitic autoimmune conditions, from lupus to Wegener's, can have preferential affects on small-fibers, large fibers, or both. In my own building here in Queens, a good friend has Bechet's disease, and the neuropathy secondary to that is mostly large fiber axonal as revealed by nerve studies and biopsy (he also goes to Cornell-Weill), and another neighbor with lupus seems to have primarily small-fiber problems. It may just be due to the individual's own circulatory tendencies in these situations.

And I haven't even gotten into the neuropathies due to certain exotic toxins, such as ciguatera poisoning, or infectious diseases such as HIV, which seems to take up residence much more often in the smaller fibers.

It just goes to show how complicated neuropathy diagnosis can be when there's no obvious "smoking gun".

(I haven't written that long a post in a LONG time.)