Abnormal dip phenomenon: a characteristic electrophysiological marker in interdigital neuropathy of the foot

Abstract

-Objective: the nerve conduction findings in interdigital neuropathy of the foot (IDN; Morton's neuroma) have rarely been reported. We analyzed the nerve conduction data in 23 patients with suspected IDN studied between 1982 and 2002. Method: Diagnosis of IDN was made on the basis of clinical features. All patients underwent routine nerve conduction studies and a near-nerve needle sensory nerve conduction study of the interdigital nerves by Oh's method in the symptomatic foot. Results: Of the 23 patients, the diagnosis of definite IDN was made in 13 cases and of possible NDN in the others cases. Nineteen were females. twenty two patients had only one nerve affected. One patient had two nerves affected. the III-IV interdigital nerve was affected in 17 cases and the II-III interdigital nerve in 7 cases. the near-nerve needle nerve conduction showed abnormality in the affected interdigital nerves in all definite IDN cases and confirmed the diagnosis of IDN in 10 cases by the abnormal dip phenomenon (a selective decrease of 50% or more in the sensory cNAP amplitude of the affected nerve compared with that of the preceding interdigital nerve). In 11 possible IDN cases, IDN was identified by the abnormal dip phenomenon. Conclusion: the near-nerve needle sensory nerve conduction of the interdigital nerves is a highly sensitive diagnostic test, and abnormal dip phenomenon is the most characteristic electrophysiological marker for the diagnosis of IDN.Key WOrDs: Morton's neuroma, metatarsalgia, interdigital neuropathy, nerve conduction.Fenômeno da diminuição de amplitude anormal: um marcador eletrofisiológico característico da neuropatia interdigital do pé resuMO -Objetivo: Os achados da condução nervosa na neuropatia interdigital do pé (NIP) têm sido raramente descritos. Nós analisamos os dados da condução nervosa de 23 pacientes com suspeita de NIP entre 1982 e 2002. Método: O diagnóstico de NIP foi clínico. todos os pacientes foram submetidos a estudos de condução nervosa de rotina e ao estudo de condução sensitiva dos nervos interdigitais com agulha justa-neural pelo método de Oh. Resultados: Dos 23 pacientes, o diagnóstico de NIP foi definitivo em 13 casos é possível nos demais. Dezenove pacientes eram mulheres e 22 tinham somente um nervo afetado. Apenas um paciente teve dois nervos comprometidos. O nervo interdigital III-IV foi afetado em 17 casos e o nervo interdigital II-III em 7 casos. A condução nervosa justa-neural foi anormal nos nervos interdigitais acometidos em todos os casos definitivos e confirmou o diagnóstico de neuropatia interdigital em 10 casos pelo fenômeno da diminuição de amplitude anormal (uma diminuição seletiva de 50% ou mais da amplitude do PANs do nervo afetado quando comparado com o nervo anterior. em 11 casos possíveis, a neuropatia interdigital foi identificada pelo fenômeno da diminuição de amplitude anormal. Conclusão: A condução nervosa sensitiva justa-neural dos nervos interdigitais do pé é um teste diagnóstico altamente sensível e o fenômeno da diminuição da amplitude anorm...

Simple electrodiagnostic method for morton neuroma

“…Almeida et al defined a gradual decrease in SNAP amplitudes from the first digital nerve to the fifth, as the “dip phenomenon,” and the selective decrease of 50% or more in SNAP amplitude of the affected nerve compared with that of the preceding interdigital nerve was called as the “abnormal dip phenomenon” . We also observed in our controls a decrease of the amplitudes from toe I to toe V, but the amplitude loss with our recording technique was too small to identify it as the dip phenomenon.…”

“…All of the patients had a definite clinical diagnosis, meeting all 3 criteria proposed by Almeida et al, The criteria are: (1) at least 1 of 2 symptoms, including localized pain between the involved metatarsal heads and/or numbness or diminished sensation in the interdigital nerve territory; (2) at least 1 of 2 findings, including Tinel sign and or pin‐prick sensory loss in the interdigital nerve territory; and (3) no evidence of distal sensory neuropathy. Each examination was made by 1 of the 2 neurologists who participated in the study.…”