Adducted thumb syndrome

Overview

Adducted Thumb Syndrome is a rare congenital disorder characterized by the persistent inward (adducted) positioning of the thumbs, typically noticeable at birth. This syndrome is often associated with other neurological or musculoskeletal abnormalities and may occur as part of broader genetic conditions, such as certain forms of arthrogryposis or central nervous system malformations. In some cases, adducted thumbs are an isolated finding, while in others, they reflect deeper developmental issues involving nerves or joints.

Causes

The causes of adducted thumb syndrome vary depending on whether the condition is isolated or syndromic. Known causes include:

• Genetic mutations: Particularly in syndromes like X-linked hydrocephalus with adducted thumbs (L1CAM gene mutation)

• Congenital joint contractures: As seen in arthrogryposis multiplex congenita

• Neuromuscular abnormalities: Disruption in motor neuron or peripheral nerve development affecting thumb positioning

• Skeletal malformations: Limiting proper thumb movement and extension

Inheritance may be autosomal dominant, autosomal recessive, or X-linked, depending on the underlying syndrome involved.

Symptoms

The primary sign of adducted thumb syndrome is the abnormal inward positioning of one or both thumbs. Additional features may vary and can include:

• Thumbs held tightly against the palm, with limited or no active extension

• Joint contractures or stiffness in other fingers or limbs

• Delayed motor development (especially fine motor skills)

• Neurological signs: In syndromic forms, such as spasticity, hypotonia, or hydrocephalus

• Other skeletal or facial anomalies, depending on the associated syndrome

Diagnosis

Diagnosis involves a thorough clinical evaluation, often starting in the neonatal period. Diagnostic steps may include:

• Physical examination: Observation of thumb posture and limb range of motion

• Neurological assessment: To detect signs of motor neuron dysfunction or associated central nervous system abnormalities

• Genetic testing: Especially if adducted thumbs are part of a suspected syndrome (e.g., L1CAM-related disorders)

• Imaging studies: Brain MRI (if hydrocephalus or brain malformations are suspected)

• EMG/Nerve conduction studies: In cases where neuromuscular disease is considered

Treatment

Treatment depends on the severity of the thumb contracture and any associated conditions. Options include:

• Physical and occupational therapy: To improve thumb mobility and hand function

• Splinting or bracing: To maintain the thumb in a more functional position

• Surgical intervention: In cases of severe contractures, tendon transfers or joint releases may be needed

• Management of associated conditions: Such as hydrocephalus, spasticity, or cognitive delays in syndromic cases

Prognosis

The prognosis for adducted thumb syndrome depends on whether the condition is isolated or part of a larger syndrome:

• Isolated cases: Often have good outcomes with physical therapy or minor surgical correction

• Syndromic cases: Prognosis varies based on the underlying genetic disorder, and may involve long-term developmental challenges or neurological impairments

Early diagnosis and intervention are key to improving hand function and overall quality of life.