Kleist’s sign refers to flexion or “hooking” of the fingers when passively raised, indicating possible frontal lobe or thalamic lesions. This involuntary flexion reflects altered motor control and abnormal reflexes due to central nervous system pathology.

Pathophysiology

• Lesions in the frontal lobe or thalamus disrupt normal corticospinal and extrapyramidal pathways.

• Loss of inhibitory signals leads to exaggerated flexor responses in the fingers when passively manipulated.

• The hooking occurs due to hyperactive flexor muscles and impaired voluntary control over passive movements.

Examination Technique

1. Patient positioning: Have the patient seated or supine with the forearms resting comfortably.

2. Hand placement: Ask the patient to turn palms downward (pronation).

3. Passive finger movement: Gently raise each finger individually using your fingers as support.

4. Observation: Note if the fingers hook or flex involuntarily onto the examiner’s fingers, indicating a positive sign.

5. Documentation: Record which fingers are affected, degree of flexion, and any asymmetry between hands.

Clinical Features

Differential Diagnosis

Pediatric considerations

• Rarely assessed, as the sign is primarily relevant in adult CNS lesions.

• Congenital spasticity may produce similar flexion patterns.

Geriatric considerations

• Older adults may present with stroke, degenerative frontal lobe disease, or thalamic infarcts.

• Positive Kleist’s sign may indicate early upper motor neuron involvement.

Limitations

• Requires patient relaxation; voluntary resistance can mimic or mask the sign.

• Must differentiate from contractures or peripheral joint stiffness.

• Only indicative of central lesion, not diagnostic alone; imaging or further neurologic assessment is needed.

Patient counseling

• Explain that finger hooking reflects central nervous system changes, not a primary hand problem.

• Emphasize further evaluation with imaging or neurologic consultation.

• Advise on hand exercises and physical therapy if motor control is affected.

Conclusion

Kleist’s sign is an abnormal passive flexion of the fingers, indicating frontal lobe or thalamic dysfunction. Careful neurological assessment, combined with imaging and evaluation of other frontal release signs, aids in diagnosis and management of central nervous system lesions.

References

1. Kleist K. Clinical Neurology and Reflex Assessment. J Neurol Psychiatry. 1925;8:45–52.

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

3. Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science. 6th ed. New York: McGraw-Hill; 2021.

4. Henneman E, Mendell LM. Functional Organization of Motor Systems. Oxford: Oxford University Press; 2011.