How Do You Know if a Nerve Was Hit During the Miradry Procedure?

Anon, although MiraDry is a non-invasive device, it works by heating the armpit tissue at the level where the sweat glands live.  You may also get some collateral injury to the sensory nerves, but this is usually temporary.  There is a nerve that courses through the armpit and provides sensation to the inner arm region.  This should heal with time (weeks-to-months), but I would definitely let your physician know what you are experiencing.

After Miradry procedure you may experience some numbness and discomfort. It usually lasts a few day but since we performed hundreds of these procedures in our office we came across a few patients (very small number) who had these sensation for several weeks. It resolved in all patients without any intervention. 

The energy that miraDry delivers can cause collateral damage to other structures in the armpit.  For example, we know miraDry affects hair follicles, causing less hair to grow after the procedure.  Depending on the patient's body habitus and the size of their armpit, temporary numbness, tingling, or a pins-and-needles sensation can occur after miraDry.  It can take several months for this to resolve, but there have been no reports of permanent damage.