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Role of Nerve Conduction Study 285

in Diabetic Patients

careful examination, because Diabetic Neuropathy done.
may be asymptomatic in a number of patients. At • In(Entrapement) mononeuropathy specific nerve
least one of each of the five criteria is needed: symp- is studied and NCS shows reduction in segmen-
toms, signs, electrodiagnostic tests, quantitative sen- tal conduction velocity and conduction block.
sory, and autonomic testing.
• For cranial neuropathies
Motor nerve conduction, F response and sensory
nerve conduction studies are commonly analysed in • 1. Facial nerve conduction- Facial Neuropathy
routine Nerve conduction study. Motor nerve conduc- • 2. Blink reflex- Trigeminal Neuropathy
tion studies are affected in a large fibre neuropathies.
The nerve conduction changes are non-specific and • 3. Visual evoked potential- Optic Neuropathy
key to the diagnosis lies in excluding other causes or • 4. BERA and VEMP to study Vestibulopathy
those superimposed on Diabetic Neuropathy.
• 5. SSEP to study posterior column- Vitamin
Entrapment neuropathies are common in diabetic B12 deficiency
patients and result in unilateral Nerve conduction
velocity changes, especially across the entrapped Advantages of Nerve conduction studies
segment of the nerve. The commonest abnormality
in diabetes is reduction in the amplitude of motor - Easily tolerated, safe
or sensory action potentials because of axonopathy. - Very sensitive to axonal loss
Pronounced slowing of Nerve conduction velocity - Very specific for demyelinating disease which is
suggests demyelinating neuropathy, which is rare- rare in Diabetes.
ly associated with diabetes; therefore pronounced
slowing of Nerve conduction velocity in a diabetic pa- Limitations:
tients should prompt investigations for an alternative
diagnosis. However, the likelihood of CIDP occurring - Routine motor and sensory conduction velocity
in diabetic patients is 11 times higher than the normal and latency measurements are from the largest
population.The Nerve conduction velocity is gradually and fastest fibers.
diminished in Diabetes neuropathy, with estimates of - Large-diameter fibers have the most myelin and
a loss of about 0.5 m/s/y. the least electrical resistance, both of which result
in faster conduction velocities.
NCS findings in Diabetic Neuropathy
- Thus, early stage of DSMPN and also neuropathies
1. In Diabetic Neuropathy evoked nerve action po- that preferentially affect only small fibers may not
tential (CMap, SNap) amplitude are reduced (Ax- reveal any abnormalities on NCSs.
onal).
- When in doubt, always think about technical fac-
2. NCS abnormalities more common in sensory tors.
than motor fibres , in the legs more than in the
arms, and in the distal more often than proximal - When in doubt, reexamine the patient.
nerve segments . - Findings should be reported in the context of the

3. Nerve conduction velocities are slower in the clinical symptoms and the referring diagnosis.
group than in healthy subjects but not upto the - When in doubt, do not overcall a diagnosis.
criteria for demyelinating neuropathy. If NCS
shows predominantly demyelinating pattern then - Always think about the clinical-electrophysiologic
diagnosis of Diabetic Neuropathy is to be ques- correlation.
tioned.
Conclusion
4. Thus, early stage of DSMPN and also neuropa- Diabetic neuropathy has been defined as presence of
thies that preferentially affect only small fibers symptoms and signs of peripheral nerve dysfunction
may not reveal any abnormalities on routine in diabetics after exclusion of other causes, which
NCSs
may range from hereditary, traumatic, compressive,
metabolic, toxic, nutritional, infectious, immune me-
Special NCS diated, neoplastic, and secondary to other systemic
• For small fibre neuropathy Sympathetic skin illnesses. Since the manifestations of diabetic neu-
response test and other autonomic test will be ropathy closely mimic chronic inflammatory demy-

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