A tuft of hair overlying the lumbar spine is a classic sign of what condition?

A tuft of hair over the lumbar spine is commonly associated with spina bifida occulta, a condition characterized by a defect in the bony encasement of the spinal cord. This defect typically results in incomplete closure of the vertebral arches, which can occur without any visible external signs. However, one of the key indicators that may be noted on physical examination is a tuft of hair, which appears at the site's location.

This hair tuft can occur due to the presence of a dermal sinus or as a result of local skin changes due to the underlying spinal defect. While other conditions, such as dermoid cysts, fibromatosis, and neurofibromatosis, can present with skin abnormalities or growths, they do not specifically associate with the tuft of hair in relation to the lumbar spine. Therefore, where the question pertains directly to the classic physical finding of a hair tuft, spina bifida occulta is the most accurate answer, as it is a well-documented sign of this congenital spinal condition.