Deep tendon reflexes in certain conditions

[kwel]

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I am actually an MS 3 on rotations, but thought this question was more suited for the step 1 forum, where people have yet to forget the science behind everything.

If I understand DTRs correctly the motor arc is a normal motor neuron. If this is so, then any condition that damages the peripheral motor neurons or NMJ should lead to decreased DTRs. These include Guillain-Barre, Polio, Botulism, MG, Lambert-Eaton. How come DTRs are preserved in some of these? Am I missing something about the physio of DTRs?

 

[thehundredthone]

I haven't heard of preserved reflexes in any LMN lesion. There are cases of GBS with intact reflexes or even hyperreflexia but then demyelination needn't necessarily halt nerve conduction.