Arachnodactyly Definition

Arachnodactyly is a condition which causes the fingers of an individual to be long, slender and look like a spider’s legs. The name “Arachnodactyly” is originally derived from two Greek words: “arachne” meaning spider and “daktylos” meaning finger. Some patients may even have spider-like toes. This physical abnormality can affect people from all countries and ethnic groups.

The condition is also referred to as also known as ‘Spider fingers.’

Arachnodactyly Causes

It can be a birth defect associated with other congenital diseases or can arise on its own. The condition is called Congenital Contractural Arachnodactyly or Beals syndrome when it develops without any underlying disorders after the birth of a child. In the majority of cases, however, it results from one of the following causes:

Marfan’s Syndrome

This is a type of connective tissue disorder affecting the skeletal system, cardiovascular system, eyes and skin.


It is a hereditary disorder which makes patients unable to process the amino acids properly. It causes movement problems, seizures, mental retardation, learning disabilities and megaloblastic anemia.

Spondylocostal Dysostosis

This rare congenital abnormality causes patients to have a short-build due to a short trunk along with various morphological defects of the vertebrae resulting from axial skeleton malsegmentation.

Ehlers-Danlos syndrome

It results from a defective collagen synthesis and causes a wide range of serious symptoms.

The problem can occur due to various other rare, genetic congenital conditions as well.

Arachnodactyly Symptoms

The principal characteristic of this condition is an abnormally long and thin appearance of the fingers when compared to the hand and palm. The fingers may also be curved to some extent. Some individuals may have unusually flexible fingers which can even be bent up to one-eighty degrees backwards. However, one should keep in mind that it is possible to have slender long fingers without any health problems.

Arachnodactyly Prevention

At present, it is not possible to keep this disorder from occurring due to an absence of preventive measures for the associated genetic diseases which generally lead to it. Individuals with spider fingers due to certain underlying disease should consider genetic counseling before having children as it can help to determine their risk of inheriting the abnormality.

Arachnodactyly Diagnosis

During the diagnosis, doctor tend to ask various questions such as

  • The time when the abnormal shape of the fingers became evident
  • Whether the patient has a family history of any genetic condition
  • Whether there is a history of early death in the patient’s family because of any genetic problems

A diagnostician may also perform certain exams to determine if the patient has an underlying disorder like Ehlers-Danlos syndrome and Marfan’s syndrome. Diagnostic tests are generally not necessary unless a doctor suspects the presence of an inherited condition.

Radiological tests may be required for detecting the physical defect in patients with Marfan’s syndrome. In this imaging test, the metacarpal index is determined by dividing the separate lengths of the last 4 metacarpals by the width of its midpoint and calculating the average of the values. The measurement is generally greater than 8.4 in people with Marfan’s Syndrome while it is less than 8 in healthy individuals.

Arachnodactyly Differential Diagnosis

It is important to rule out the presence of the following conditions, which produce similar symptoms, while making a diagnosis of spider fingers:

  • Marfan’s Syndrome
  • Lutembacher’s Syndrome
  • Homocystinuria
  • Spondylocostal Dysostosis
  • MASS Syndrome (inheritable disorder that involves the Aorta, Mitral valve, Skeleton and Skin)
  • Achard Syndrome
  • Van der Hoeve’s Syndrome

Arachnodactyly Treatment and Management


It is a physical deformity with no treatment. However, in most cases it is associated with some other serious genetic disorder which can lead to a number of serious physical and mental problems if left untreated. Due to this reason, a child with spider fingers should be examined properly to determine if he or she has any serious underlying cause. Individuals who have abnormally thin and long fingers due to Marfan’s syndrome should be treated immediately in order to avoid various vision problems and cardiac disorders.

Arachnodactyly Prognosis

The prognosis of this condition depends on the original underlying disease which is causing the spider fingers. Arachnodactyly itself does not have a prognosis as it is not possible to treat it medically.

Arachnodactyly Images

The following photos show how the condition changes the appearance of the appendages.

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Arachnodactyly requires early detection and medical attention to determine if a patient has a more serious underlying disease. Individuals with spider fingers caused by a serious genetic problem should be treated properly so that they can lead as normal a life as possible.

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