Epidermal nerve fiber (ENF) density and morphology are used to diagnose small fiber involvement in diabetic and other small fiber neuropathies. ENF density and summed length of ENFs per epidermal surface area are reduced in diabetic subjects. Furthermore, based on mainly visual inspection, it has been reported that ENFs of subjects with diabetic neuropathy seem to appear more clustered than ENFs of healthy subjects. Therefore, it is important to understand the spatial structure of ENFs in healthy and diseased subjects.
We have investigated the spatial structure of ENF entry points, which are the locations where the nerves enter the epidermis (the outmost living layer of the skin), and ENF end points, which are the terminal nodes of ENFs. The study is based on suction skin blister specimens from two body locations (with replicates) of 32 healthy subjects and 25 subjects with diabetic neuropathy. The ENF entry (end) points are regarded as a realization of a spatial point process and Ripley\'s K function is used as a summary statistic for the second-order spatial structure.
The effect of disease status and some other covariates (gender, age, body mass index) on the degree of clustering of ENF entry (end) points as well as the effect of the individual variation are characterized by a hierarchical Bayesian approach. The work is joint with Mari Myllymaki and Aki Vehtari (Aalto University, Finland) and Ioanna Panoutsopoulou (University of Minnesota).