How do we check vibration on the toe using the Minnesota Neuropathy Screening Instrument (MNSI)?

Vibration Testing on the Toe Using the Minnesota Neuropathy Screening Instrument (MNSI)

Apply a 128-Hz tuning fork perpendicularly on the bony prominence of the dorsal side of the distal phalanx (tip) of the great toe, using constant pressure, and score the patient's ability to perceive the vibration. 1

Preparation and Patient Setup

• Conduct the examination in a quiet, relaxed environment to minimize distractions and ensure accurate responses 1
• First demonstrate the vibration sensation on the patient's wrists, elbows, or clavicle so they understand what to expect before testing the feet 1
• The patient must not be able to see whether or where you are applying the tuning fork during the actual examination 1

Technique for Vibration Testing

• Use a 128-Hz tuning fork specifically for this assessment 1
• Strike the tuning fork to activate vibration, then apply it on the bony part on the dorsal side of the distal phalanx of the first toe (great toe) 1
• Apply the tuning fork perpendicularly to the skin surface with constant pressure 1
• Hold the tuning fork in place and ask the patient if they can feel the vibration 1

Scoring Protocol

• Repeat the application twice at the same site, but alternate with at least one 'mock' application where the tuning fork is not vibrating (total of three applications per site) 1
• Ask the patient to identify when they feel vibration versus when they do not 1
• The test is positive (normal) if the patient correctly answers at least 2 out of 3 applications 1
• The test is negative (abnormal) if the patient has 2 out of 3 incorrect answers, indicating the patient is at risk for ulceration 1

MNSI Scoring System

• In the MNSI physical examination component, vibration perception is scored as either 0 (present/normal) or 1 (reduced or absent/abnormal) for each foot 2
• The MNSI physical examination includes foot appearance, ulceration, ankle reflexes, and vibration perception, with a maximum total score of 8 points 2
• An MNSI score ≥2.5 is the cut-off for diagnosing peripheral diabetic neuropathy, with 75% specificity and 78.6% sensitivity 2

Proximal Testing if Abnormal

• If the patient is unable to sense vibrations on the great toe, repeat the test more proximally at the medial malleolus (ankle) and tibial tuberosity to determine the level of sensory loss 1

Common Pitfalls to Avoid

• Do not use insufficient force when applying the tuning fork—it must make firm contact with the bony prominence 1
• Avoid testing over soft tissue, calluses, ulcers, or scars—always test on bony prominences 1
• Do not skip the mock applications—these are essential to detect patients who may be guessing or responding inappropriately 1
• Provide positive feedback and encouragement during testing to maintain patient engagement 1