The lines on your hand, known as palmar creases, are folds in the skin that form during fetal development. While most individuals exhibit several distinct creases across their palms, a variation sometimes occurs where these lines merge into a single, continuous fold. This anatomical feature is called a “single palmar crease” or “single transverse palmar crease.”
Understanding Hand Creases
The human palm displays three primary creases: the distal palmar crease, the proximal palmar crease, and the thenar crease. The distal palmar crease, also known as the heart line, runs across the upper part of the palm, near the base of the fingers. It begins close to the little finger and extends towards the base of the middle or index finger.
The proximal palmar crease, also called the head line, is positioned below the distal crease and runs somewhat parallel to it across the middle of the palm. The thenar crease, referred to as the life line, curves around the base of the thumb, delineating the thenar eminence, the fleshy mound at the thumb’s base. These creases develop to allow the hand’s skin to stretch and fold without bunching during grasping and other movements.
The Single Palmar Crease
A single palmar crease, sometimes called a “simian crease,” forms when the distal and proximal palmar creases fuse into one continuous line extending across the palm. This variation is present in a small percentage of the general population, estimated to be between 1.5% and 4%. It can appear on one hand (unilaterally) or both hands (bilaterally).
In many instances, a single palmar crease is an isolated anatomical variation that has no associated medical significance. This trait can be inherited and is more commonly observed in males than females, with males being twice as likely to have it. The crease develops in utero.
Medical Associations
While a single palmar crease is a benign finding, its presence can be associated with certain genetic conditions or developmental syndromes. It is observed more often in individuals with Down syndrome (Trisomy 21), appearing in approximately 45% to 60% of affected individuals. Other conditions where a single palmar crease may be seen include Fetal Alcohol Syndrome.
Aarskog-Scott syndrome, an X-linked genetic disorder primarily affecting males, also shows a higher incidence of single palmar creases among its various physical characteristics, which can include distinctive facial features, short stature, and hand abnormalities. Other conditions linked to a single palmar crease include:
- Cohen syndrome
- Trisomy 13
- Rubella syndrome
- Turner syndrome
- Klinefelter syndrome
- Pseudohypoparathyroidism
- Cri du chat syndrome
The presence of a single palmar crease alone is not sufficient for diagnosing any of these conditions; it is one of several potential physical indicators that may prompt further medical evaluation when observed alongside other signs or symptoms.
When to Consult a Doctor
Seeking medical advice regarding a single palmar crease is recommended if it is observed in an infant or child who also exhibits other developmental delays, unusual physical features, or health concerns. A healthcare provider may inquire about family history or if other family members have the crease without additional symptoms. In such cases, a complete physical examination and medical history are used to determine if further testing, such as genetic analysis, is appropriate. However, if a single palmar crease is the only finding in an otherwise healthy individual, it is not a cause for concern.