Beevor's sign is the movement of the navel

Navel

The navel is a scar on the abdomen caused when the umbilical cord is removed from a newborn baby...

 towards the head on flexing the neck

Neck

The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...

. It is caused by weakness of the lower abdominal muscles.

Pathophysiology

Beevor’s sign is characteristic of spinal cord

Spinal cord

The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...

 injury between T6 and T10 levels. This occurs because the upper abdominal muscle such as the Rectus Abdominus are intact at the top of the abdomen but weak at the lower portion. Thus when the patient is asked to do a sit up only the upper muscles contract pulling the umbilicus toward the head in patients who are abnormal. It has also been described in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis , also referred to as Lou Gehrig's disease, is a form of motor neuron disease caused by the degeneration of upper and lower neurons, located in the ventral horn of the spinal cord and the cortical neurons that provide their efferent input...

 and facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy , which is also known as Landouzy-Dejerine, is a usually autosomal dominant inherited form of muscular dystrophy that initially affects the skeletal muscles of the face , scapula and upper arms...

.