The fan sign is a component of the Babinski reflex, characterized by the spreading (fanning) of the toes in response to firm stimulation of the sole of the foot. It is considered a positive sign of upper motor neuron (UMN) lesions, particularly involving the corticospinal (pyramidal) tract.

Pathophysiology

• In a healthy adult, stimulation of the sole normally produces toe flexion due to inhibitory control from the corticospinal tract.

• Damage to the pyramidal tract removes this inhibition, leading to extensor responses such as:

  • Dorsiflexion of the great toe

  • Fanning of the other toes (fan sign)

• This response indicates disinhibition of spinal reflex arcs, commonly seen in:

  • Stroke

  • Multiple sclerosis

  • Traumatic brain injury

  • Spastic hemiplegia

Examination Technique

1. Patient Positioning: Patient lies supine with legs extended and relaxed.

2. Stimulation: Use the blunt end of a reflex hammer or finger to firmly stroke the lateral aspect of the sole, moving from the heel toward the toes.

3. Assessment:

   • Observe the great toe for dorsiflexion.

   • Observe the other toes for spreading apart (fan sign).

   • Document unilateral or bilateral presence.

Clinical Utility

• Indicator of upper motor neuron lesions: Often assessed alongside Babinski, Chaddock, Oppenheim, and Gordon signs.

• Early detection: Helpful in diagnosing pyramidal tract involvement in stroke, spinal cord lesions, or demyelinating diseases.

• Monitoring progression: Can be used to track neurological recovery or deterioration.

Differential Diagnosis

Pediatric considerations

• Normal up to ~7 months due to immature corticospinal pathways.

• Post-infancy: positive fan sign suggests neurological pathology.

Geriatric considerations

• Commonly assessed in stroke or neurodegenerative disorders.

• Often accompanied by spasticity, clonus, or other UMN signs.

Limitations

• False positives may occur in infants, anxious, or uncooperative patients.

• Should not be used in isolation; interpret with other neurological findings.

Patient counseling

• Explain that toe movement is a normal reflex test, part of neurological assessment.

• Reassure that the finding helps identify underlying nerve or brain conditions.

• Advise follow-up evaluation if abnormal responses are noted.

Conclusion

The fan sign is a classic neurological marker of upper motor neuron dysfunction, representing the fanning of toes during the Babinski reflex. It aids in the diagnosis and localization of pyramidal tract lesions when performed correctly and interpreted alongside other clinical findings.

References

1. Babinski J. Contribution à l’étude des réflexes cutanés plantaires. Rev Neurol. 1896;4:97–112.

2. Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science. 5th ed. New York: McGraw-Hill; 2013.

3. Ropper AH, Samuels MA, Klein JP. Adams and Victor’s Principles of Neurology. 11th ed. New York: McGraw-Hill; 2021.

4. Frowein RA, Mumenthaler M. Clinical examination of pyramidal signs. Neurol Clin. 2000;18:595–610.