In 2007 we introduced a grading system of severity of distal symmetric diabetic neuropathy (DN) by nerve conduction study (NCS) of the lower limb: sensory NCS of the sural nerve and motor NCS of the tibial nerve. Its diagnostic algorism was published on this journal in 2013; Recently, the classification system is sometimes referred and utilized under the name of Baba’s DN classification (BDC) by the Japanese physicians and researchers. The BDC consists of five stages; BDC-0 (normal): no NCS abnormalities, BDC-1 (mildly abnormal): delay in any of MCV, SCV, F-wave latency, and/or positive a-waves, BDC-2 (moderately abnormal): fall in sural SNAP amplitude less than 5 μV, BDC-3 (severely abnormal): fall in plantar muscle-CMAP amplitude to 2–5 mV, BDC-4 (ultimately abnormal): fall in plantar muscle-CMAP less than 2 mV. To test validity of the BDC system, we conducted 5-year prospective study on incident diabetic foot (DF) by the BDC in type-2 diabetic patients. In addition, incident ischemic stroke (IS) and ischemic heart disease (IHD), and eventual premature death (EPD) were counted. Among the diabetic patients examined by NCS during 2007 to 2011, 286 subjects were diagnosed by BDC and followed five years or until their EPD. The subjects categorized were as follows; BDC-0: 8%, BDC-1: 37%, BDC-2: 37%, BDC-3: 11%, BDC-4: 7%. Cumulative occurrence of DF during the 5 years was; BDC-0: 0%, BDC-1: 0%, BDC-2: 4%, BDC-3: 22%, BDC-4: 38%. Any of DF, IHD and/or IS happened as follows; BDC-0: 0%, BDC-1: 3%, BDC-2: 24%, BDC-3: 53%, BDC-4: 57%. There was no EPD from BDC-0, -1, and -2 groups (n=133), while three from BDC-3 group (n=32) and two from BDC-4 group (n=21) were found dead unexpectedly, or died of sepsis after the recent DF. In conclusion, the BDC works satisfactory not only as grading system of current DN severity, but also for evaluation of the risk of FD, IHD, IS and EPD.
Several studies have shown the failure of excitation-contraction (E-C) coupling in myasthenia gravis (MG). However, there had been few useful methods to measure E-C coupling in vivo. In 2000s, we developed new E-C coupling testing procedures using accelerometer to record movement-related potentials (MRPs). The compound muscle action potentials (CMAPs) and MRPs were recorded simultaneously after stimulating the dominant nerve, and the E-C coupling time (ECCT) was calculated by the latency difference between CMAP and MRP. Moreover, the amplitude of MRP (=maximum acceleration) was analyzed to examine the twitch force of innervated muscles. The new method has been applied to masseter and jaw movement after trigeminal nerve stimulation (Imai’s method), or abductor pollicis brevis (APB) muscle and thumb movement after median nerve stimulation. As a result, we reported several interesting findings in MG: (1) impaired E-C coupling contributes to muscle weakness apart from neuromuscular transmission in the masseter; (2) anti-ryanodine receptor (RyR) antibody contributes to E-C coupling impairment in the masseter; (3) the early effect of tacrolimus may imply a pharmacological enhancement of RyR function to improve E-C coupling; (4) post-tetanic potentiation of APB muscle twitch is diminished, suggesting impaired E-C coupling; (5) the ice-pack test induces a prolonged effect of ameliorating impaired E-C coupling.
Low-density lipoprotein receptor-related protein 4 (LRP4) is crucial membrane protein in the development and function of neuromuscular junctions and motor neurons. And, it is currently known myasthenia gravis (MG) is caused by antibodies to the acetylcholine receptor (AChR), muscle-specific kinase (MuSK), and LRP4. MuSK and LRP4 are coreceptors for agrin in the signaling pathway that causes clustering of AChR. We demonstrated anti-LRP4 antibodies played a key role in MG. LRP4 is essential for maintaining the structural and functional integrity of the neuromuscular junction and that loss of muscle LRP4 in adulthood alone is sufficient to cause myasthenic symptoms. MG with anti-LRP4 antibodies is considered a rare subtype of MG, however, LRP4 autoantibodies have been recently detected in some motor neuron disease patients, and LRP4 is required for presynaptic and postsynaptic differentiation. We developed the luciferase immunoprecipitation systems for LRP4 autoantibodies detection and with this assay we studied for four years the sera from Japanese patients who had been suspected of MG or other neurological diseases with general myasthenia and/or muscle weakness. The clinical and therapeutic implications of the anti-LRP4 antibody positivity remain to be clarified, and further studies are necessary to elucidate the pathogenic potential of these autoantibodies.