Anterior interosseous syndrome is a medical condition in which damage to the

anterior interosseous nerve The anterior interosseous nerve (volar interosseous nerve) is a branch of the median nerve that supplies the deep muscles on the anterior of the forearm, except the ulnar (medial) half of the flexor digitorum profundus. Its nerve roots come from C ...

(AIN), a distal motor and sensory branch of the

median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has cont ...

, classically with severe weakness of the pincer movement of the thumb and

index finger The index finger (also referred to as forefinger, first finger, second finger, pointer finger, trigger finger, digitus secundus, digitus II, and many other terms) is the second digit of a human hand. It is located between the thumb and the m ...

, and can cause transient pain in the wrist (the terminal, sensory branch of the AIN innervates the bones of the

carpal tunnel In the human body, the carpal tunnel or carpal canal is a flattened body cavity on the flexor ( palmar/volar) side of the wrist, bounded by the carpal bones and flexor retinaculum. It forms the passageway that transmits the median nerve and the ...

). Most cases of AIN syndrome are now thought to be due to a transient

neuritis Neuritis (), from the Greek ), is inflammation of a nerve or the general inflammation of the peripheral nervous system. Inflammation, and frequently concomitant demyelination, cause impaired transmission of neural signals and leads to aberrant ne ...

, although compression of the AIN in the forearm is a risk, such as pressure on the forearm from immobilization after shoulder surgery. Trauma to the median nerve or around the proximal median nerve have also been reported as causes of AIN syndrome. Studies are limited, and no

randomized controlled trial A randomized controlled trial (or randomized control trial; RCT) is a form of scientific experiment used to control factors not under direct experimental control. Examples of RCTs are clinical trials that compare the effects of drugs, surgical ...

s have been performed regarding the treatment of AIN syndrome. While the natural history of AIN syndrome is not fully understood, studies following patients who have been treated without surgery show that symptoms can resolve starting as late as one year after onset. Other retrospective studies have concluded that there is no difference in outcome in surgically versus nonsurgically treated patients. The role of surgery in AIN syndrome remains controversial. Indications for considering surgery include a known space-occupying lesion that is compressing the nerve (a mass) or fascial compression, and persistent symptoms beyond 1 year of conservative treatment.

Symptoms and signs

The findings are weakness in bending (flexion) the tips of the thumb and index finger.

Clinical signs

In a pure lesion of the anterior interosseous nerve there is weakness of the long flexor muscle of the thumb (

Flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is uniq ...

), the deep flexor muscles of the index and middle fingers (

Flexor digitorum profundus The flexor digitorum profundus or flexor digitorum communis profundus is a muscle in the forearm of humans that flexes the fingers (also known as digits). It is considered an Muscles of the hand#Extrinsic, extrinsic hand muscle because it acts on ...

I & II).

Causes

Injuries of the forearm with compression of the nerve from swelling is the most common cause: examples include supracondylar fractures, often associated with haemorrhage into the deep musculature; injury secondary to open reduction of a forearm fracture; or dislocation of the elbow.⁠⁠Van Der Wurff, P, R H Hagmeyer, and W Rijnders. "Case Study: Isolated Anterior Interosseous Nerve Paralysis: The - Kiloh-Nevin Syndrome." The Journal of Orthopaedic and Sports Physical Therapy 6, no. 3 (1984): 178-80. . Direct trauma from a penetrating injury such as a stab wound is a possible cause for the syndrome. Fibrous bands or Arcuate ligament~arcuate (curved) ligaments may entrap the median as well as the anterior interosseous nerve, in which case a patient may experience hand numbness as well as wrist pain.⁠⁠Rask, M R. "Anterior interosseous nerve entrapment: (Kiloh-Nevin syndrome) report of seven cases." Clinical Orthopaedics and Related Research, no. 142: 176-81. . Very similar syndromes can be caused by more proximal lesions, such as

brachial plexus The brachial plexus is a network of nerves (nerve plexus) formed by the anterior rami of the lower four Spinal nerve#Cervical nerves, cervical nerves and first Spinal nerve#Thoracic nerves, thoracic nerve (cervical spinal nerve 5, C5, Cervical spi ...

.⁠Schollen, Wilfried, Ilse Degreef, and Luc De Smet. "Kiloh-Nevin syndrome: a compression neuropathy or brachial plexus neuritis?." Acta Orthopaedica Belgica 73, no. 3 (June 2007): 315-8. . Anterior interosseous nerve entrapment or compression injury remains a difficult clinical diagnosis because it is mainly a motor nerve problem, and the syndrome is often mistaken for index finger and/or thumb tendon injury.⁠Rosenberg, J N. "Anterior interosseous/median nerve latency ratio." Archives of Physical Medicine and Rehabilitation 71, no. 3 (March 1990): 228-30. . Although there is still controversy among

upper extremity The upper Limb (anatomy), limbs or upper extremities are the forelimbs of an upright posture, upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digit (anatomy), digits, including all the musc ...

surgeons, AIN syndrome is now regarded as a neuritis (inflammation of the nerve) in most cases; this is similar to Parsonage–Turner syndrome. Although the exact

etiology Etiology (; alternatively spelled aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek word ''()'', meaning "giving a reason for" (). More completely, etiology is the study of the causes, origins ...

is unknown, there is evidence that it is caused by an immune-mediated response that can follow other illnesses, such as

pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of Cough#Classification, productive or dry cough, ches ...

or severe viral illness.

Anatomy

The

is a branch of the median nerve, with a large sensory branch to the wrist bones, which arises just below the elbow. It passes distally, anteriorly along the

interosseous membrane An interosseous membrane is a thick dense fibrous sheet of connective tissue that spans the space between two bones, forming a type of syndesmosis joint. Interosseous membranes in the human body: * Interosseous membrane of forearm * Interosseo ...

and innervates

flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is uniq ...

flexor digitorum profundus The flexor digitorum profundus or flexor digitorum communis profundus is a muscle in the forearm of humans that flexes the fingers (also known as digits). It is considered an Muscles of the hand#Extrinsic, extrinsic hand muscle because it acts on ...

to index and middle finger as well as pronator quadratus, and supplies sensory feedback from the wrist bones, i.e. the carpal tunnel, not skin.

Diagnosis

Electrophysiologic testing is an essential part of the evaluation of anterior interosseous nerve syndrome. Nerve conduction studies may be normal or show pronator quadratus latency.⁠⁠

Electromyography Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyo ...

(EMG) is generally most useful and will reveal abnormalities in the flexor pollicis longus, flexor digitorum profundus I and II and pronator quadratus muscles.⁠⁠Gessini, L, L Bove, B Jandolo, C Landucci, and A Pietrangeli. " nterior interosseus nerve syndrome (Kiloh-Nevin) (author's transl)" Rivista Di Patologia Nervosa E Mentale 101, no. 1: 1-11. . The role or

MRI Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and rad ...

and

ultrasound imaging Medical ultrasound includes diagnostic techniques (mainly imaging) using ultrasound, as well as therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal body structures such as tendons, muscles, join ...

in the diagnosis of Kiloh-Nevin syndrome is unclear.⁠ If asked to make the "OK" sign, patients will make a triangle sign instead. This 'pinch-test' exposes the weakness of the flexor pollicis longus muscle and the flexor digitorum profundus I leading to weakness of the flexion of the distal phalanges of the thumb and index finger. This results in impairment of the pincer movement and the patient will have difficulty picking up a small item, such as a coin, from a flat surface.

Treatment

Surgical decompression can give excellent results if the clinical picture and the EMG suggest a compression neuropathy.Stern, M B. "The anterior interosseous nerve syndrome (the Kiloh-Nevin syndrome). Report and follow-up study of three cases." Clinical Orthopaedics and Related Research, no. 187: 223-7. . In brachial plexus neuritis, conservative management may be more appropriate. Spontaneous recovery has been reported, but is said to be delayed and incomplete. There may be a role for

physiotherapy Physical therapy (PT), also known as physiotherapy, is a healthcare profession, as well as the care provided by physical therapists who promote, maintain, or restore health through patient education, physical intervention, disease preventio ...

in some cases, and this should be directed specifically towards the pattern of pain and symptoms. Soft tissue massage, stretches and exercises to directly mobilise the nerve tissue may be used.⁠ Studies following patients who have been treated without surgery show that symptoms can resolve starting as late as one year after onset. Other retrospective studies have concluded that there is no difference in outcome in surgically versus nonsurgically treated patients. The role of surgery in AIN syndrome remains controversial. Indications for considering surgery include a known space-occupying lesion that is compressing the nerve (a mass) or fascial compression and persistent symptoms beyond 1 year of conservative treatment.

History

The syndrome was first described by Parsonage and Turner in 1948⁠ and further defined as isolated lesion of the anterior interosseous nerve by Leslie Gordon Kiloh and Samuel Nevin in 1952.KILOH, L G, and S NEVIN. "Isolated neuritis of the anterior interosseous nerve." British Medical Journal 1, no. 4763 (April 19, 1952): 850-1. .

References

External links

{{PNS diseases of the nervous system Neurological disorders Mononeuropathies of upper limb Syndromes