Crichton-Browne sign

The Crichton-Browne sign, also known as the "thumb sign," is a medical diagnostic sign used to assess the presence of upper motor neuron lesions. It is named after Sir James Crichton-Browne, a prominent British neurologist who first described the sign in the late 19th century.

Description

The Crichton-Browne sign is observed during the examination of a patient's hand and wrist. It involves the extension of the thumb in response to passive flexion of the fingers. Normally, when the fingers are flexed, the thumb automatically flexes as well. However, in individuals with upper motor neuron lesions, the thumb extends instead of flexing, resulting in the characteristic "thumb sign."

Clinical Significance

The presence of the Crichton-Browne sign indicates damage or dysfunction of the upper motor neurons, which are responsible for transmitting signals from the brain to the spinal cord. Upper motor neuron lesions can occur due to various conditions, including stroke, multiple sclerosis, spinal cord injury, and certain neurodegenerative disorders.

The Crichton-Browne sign is particularly useful in diagnosing conditions such as corticospinal tract lesions, which affect the descending motor pathways. It helps differentiate upper motor neuron lesions from lower motor neuron lesions, which involve damage to the nerves that directly innervate the muscles.

Interpretation

When the Crichton-Browne sign is present, it suggests an interruption in the normal inhibitory control of the thumb extensor muscles by the upper motor neurons. This loss of inhibition leads to the abnormal extension of the thumb when the fingers are flexed.

It is important to note that the Crichton-Browne sign is not specific to any particular condition and should be interpreted in conjunction with other clinical findings and diagnostic tests. Additional assessments, such as imaging studies and electromyography, may be necessary to determine the underlying cause of the upper motor neuron lesion.

References

1. Crichton-Browne J. On the so-called "thumb sign" in hemiplegia. Brain. 1888;11(1):1-9. doi:10.1093/brain/11.1.1

2. Kimura J. Electrodiagnosis in Diseases of Nerve and Muscle: Principles and Practice. 4th ed. Oxford University Press; 2013.

See Also

• Upper motor neuron
• Lower motor neuron
• Corticospinal tract
• Neurodegenerative disorders