Autonomic Evaluation Is Independent of Somatic Evaluation for Small Fiber Neuropathy (S26.002)

OBJECTIVE: To study the correlation between different diagnostic tests for small fiber neuropathy (SFN): quantitative sudomotor axon reflex test (QSART), quantitative sensory testing (QST) and skin biopsy (IENFD). BACKGROUND: In a prior study, adding QSART (autonomic evaluation) to a combination of clinical examination, QST and IENFD (somatic evaluation) significantly increased diagnostic sensitivity for SFN. These findings suggested that autonomic and somatic assessment for SFN may be complementary. To support this hypothesis, it is important to demonstrate that 9autonomic9 and 9somatic9 evaluation of SFN are independent of each other. DESIGN/METHODS: 73 patients with clinically suspected sensory neuropathy without motor weakness but normal nerve conduction studies underwent blinded QSART, QST and skin biopsy for diagnosis of SFN. Linear regression analysis was performed to assess the association between the values of QSART (uL/cm2), QST (JND) and IENFD (fibers/mm). For QST, the comparison was done separately between vibration JND, cooling JND, HP 0.5 JND, HP 5.0-0.5 JND and HP 5.0 JND. RESULTS: There was a linear but inverse correlation between vibration JND and ankle IENFD (r = -0.37; p=0.018) and cooling JND and ankle IENFD (r = -0.30; p=0.03). However, there was no association between HP 0.5, HP 5.0-0.5 or HP 5.0 and ankle IENFD. There was also no correlation between foot QSART and ankle IENFD, leg QSART and thigh IENFD or foot QSART and heat pain measures. CONCLUSIONS: There was no significant association between 9autonomic9 and 9somatic9 components of small nerve fibers. This supports the concept that assessment of autonomic and somatic functions of SFN is complementary and should be done concurrently. However, various modalities of 9somatic9 functions are not independent. Disclosure: Dr. Thaisetthawatkul has nothing to disclose. Dr. Fernandes has nothing to disclose. Dr. Herrmann has received personal compensation for activities with Pfizer Inc as an consultant.