Comparison of intraepidermal nerve fibre density among different age groups in healthy dogs.

The intraepidermal nerve fiber (IENF) density is a key point in assessing pain perception in mammals. Its value tends to be different when addressed to different classes of age and different anatomical compartments. This study investigated the physiological range of IENF density within the hind limb in healthy dogs of different ages, in order to be aware of cutaneous pain perception expected in clinical practice and trace a starting point for the potential use of this method in the diagnosis of peripheral neuropathies. FFPE 8 mm punches on the hind limb were obtained from fifteen dogs equally divided into three classes of age: (1) newborns, (2) adults, (3) old dogs. The identification of intraepidermal nerve fibers was carried out by indirect immunofluorescence (IIF) and immunohistochemistry (IHC), using PGP 9.5 as a marker. The newborn dogs showed consistently higher IENF density compared to adult and old dogs, statistically significant when referred to the hind limb proximal site. A consistent gradient in IENF density between the proximal and the distal site of the hind limb was also observed in all classes of age. This study highlights the higher number of IENF in newborns compared with adults and old dogs. For this reason, pain perception in newborn dogs should be reconsidered in healthcare and medical procedures.