I saw a patient on rounds the other day w/ MG (Myasthenia Gravis) and it was mentioned that DTR (deep tendon reflexes) are preserved. I've been going over it in my head and I am confused why they would be preserved.
Textbooks are specifically pointing out that in classic MG, DTR is remained and therefore this is one of the findings that we can use to differentiate MG from Lambert–Eaton Myasthenic Syndrome. I am wondering why DTR is remained in classic MG?
ANSWER TO THE QUESTİON:
In MG as in LEMS the afferent limb of the reflex ark is unaffected as is the efferent up until the neuromuscular junction. The explanation of preserved reflexes in MG is that the initial barrage arrives at a rested neuromuscular junction. The initial release of acetylcholine is larger than later in a train of impulses and this is sufficient to overcome any deficit in the number of acetylcholine receptors. Only brief transmission is needed to provide the mechanical response, and this occurs before fatigability can set in. (Source: https://onlinelibrary.wiley.com/doi/abs/10.1002/mus.880180821