Warming Cold Hands and Feet for Nerve Conduction Studies

By Chris Faubel, M.D. —

The importance of warming cold hands and feet is essential when performing reliable nerve conduction studies (NCS).  Why?

Decreased limb temperatures affect the latency, amplitude, conduction velocity, and duration of both sensory and motor neurons; in my experience, sensory neurons are MUCH more sensitive to cold temperatures.

Effects of COLD Hands/Feet

Latency

• Prolonged
• Takes longer for the generated impulse to travel down the nerve and get read by the recording electrodes (the rings in my upper extremity case)
• Therefore, a cold arm/hand will show a falsely slow median and ulnar sensory peak latency, which would lead to incorrect diagnoses of carpal tunnel syndrome (median neuropathy) or ulnar neuropathy

Amplitude

• Increased
• The typical sensory nerve action potential (SNAP) [seen in the images below and to the right] is a summation of the varying times it takes the individual sensory neurons to depolarize, travel down the nerve, and picked up by the recording electrodes on the fingers.
• With cold temperatures, the faster neurons slow down and travel with some of the other neurons, which leads to a taller peak amplitude.
• Sensory > motor
• This is shown best in the sensory median nerve image below.

Conduction Velocity

• Decreased
• Explained above

Duration

• Increased
• Duration is the time from onset latency until it returns to baseline.  As seen in the images I posted the top waveform is more “spread out”

Cold hands and feet mean cold nerves, and cold nerves show abnormally slow nerve conduction results –> Falsely slow readings

Ways To Measure The Skin Temperature

1. Infrared temperature gun thermometer:  This is my favorite because it is so quick and easy.  I have my medical assistant take the temperature with the red laser pointed at the carpal tunnel on the ventral side of the hands.  If it is below 32 degrees C, the patient gets the hands warmed up.  Here’s an example of one from Amazon.com (not the exact one I use).
2. Temperature probe from the EMG machine:  MUCH more cumbersome.  Have to worry about another cord in the way while performing the exam.  Takes longer to get a steady temperature reading.

Ways To Warm Up Cold Hands

1. Warm running water from sink:  Make sure the patient gets the warm water up to their wrists.  Will take about a minute or two under fairly hot running water.
2. Hydrocollator:  Some docs have kept a hydrocollator in the office with hot packs.  For instance…link.  May be the only good option for warming cold feet.
3. Chemical hot packs:  The ones you squeeze until you hear the pop that warms up the pack.  Disposable.  Not nearly as quick as the above options.  For instance…link.