Study of the efficacy of the Distribution of F-latency (DFL) in the diagnosis of cervical spondylosis

Abstract

Distribution of F-Latency (DFL) is a new parameter in peripheral nerve conduction measurement initiated by our extended group in Dhaka University which has been established to give a Distribution of Conduction Velocity (DCV) of motor nerve fibres in a peripheral nerve trunk as its approximate mirror image. An important application of this new technique, developed by the same group, is the detection of Cervical Spondylotic Neuropathy at an early stage through an evaluation of the pattern of DFL. Typically a single sharp peak corresponds to normalcy while double peak or a broad peak represents pathology. The definition of a broad peak was formalised through an earlier study by the extended group in collaboration with a group in Singapore. The current study is an exercise in validating DFL as a screening tool for CSN by comparing the data obtained from an extended pool of subjects (62 median nerves of 31 persons) against corresponding MRI findings through a double blind study. Subject selection was done randomly to fall under two age groups: 20 to 50 yrs, and above 50 yrs. A 1.5 Tesla MRI scanner and a home built Computerised EMG equipment were used for this study. The data were analysed with two slightly different approaches. In one, a mild compression of the spinal cord or a nerve root, as assessed through MRI, was counted as negative for CSN. In the other, the same was counted as positive. The sensitivities thus calculated for both the age groups combined (62 nerves) were 82% and 78% respectively while the specificities were 28% and 50% respectively. This suggested the consideration of abnormality for mild compression. Based on this, analyses for the lower age group (20-50 yrs, 44 nerves of 22 subjects) gave a sensitivity of 73% and a specificity of 50% while for the higher age group (>50 yrs, 18 nerves of 9 subjects), the sensitivity was 89%. The specificity could not be determined for this group as none came out as true negative and false positive. A surprising find of this study was the high prevalence (91%) of CSN in the younger age group, based on the MRI results, which needs further epidemiologic study. The present study establishes DFL on a stronger footing for assessment of cervical spondylotic neuropathy, whether due to spinal cord or nerve root compression. With further development, the performance is expected to improve making it more effective. . Being a non-invasive technique requiring virtually zero expenditure in consumables, it promises greater access to patients, and could be used for extensive prevalence study. The capability of DFL in detecting subclinical stages of CSN holds a promise as an awareness development tool alongside screening for prevalence of neuropathy. Those individuals who are diagnosed as positive for CSN and are still asymptomatic could be persuaded to make changes of lifestyle to lessen the chance of progression of their health condition. The main conclusion of the work is that DFL can not only be a cost effective screening test for CSN but also be instrumental in building awareness about preventive lifestyles in the general population (both young and old). The favourable results obtained here inspire confidence that this technique would prove its robustness and over time gain widespread acceptance.