Ataxia, from the Greek word for 'without order', describes incoordination of movement, speech and posture. This can be due to cerebellar or posterior sensory pathway problems. Cerebellar causes are more common in children. In cerebellar ataxia there is an unsteady wide-based gait, difficulty in performing repetitive and alternating movements (dysdiadochokinesis), overshooting of target-directed movement (dysmetria) and an intention tremor which becomes more pronounced when the child puts more effort into trying to hold a posture. The gait has a wide base to provide stability to compensate for the truncal ataxia. There may be associated wobble of the head, nystagmus and speech impairment with a scanning dysarthria. Cerebellar ataxia may be caused by various insults to the cerebellum:
• acute, from medication and drugs, including alcohol and solvent abuse
• post-viral, particularly after varicella infection
• posterior fossa lesions or tumours, e.g. medulloblastoma
• genetic and degenerative disorders, e.g. ataxic cerebral palsy, Friedreich's ataxia and ataxia-telangiectasia
Friedreich's ataxia
This is an autosomal recessive condition The gene mutation (Frataxin) is an example of a trinucleotide repeat disorder. It presents with worsening ataxia, distal wasting in the legs, absent lower limb reflexes but extensor plantar responses because of pyramidal involvement, pes cavus and dysarthria. This is similar to the hereditary motor sensory neuropathies, but in Friedreich's ataxia there is impairment of joint position and vibration sense, extensor plantars and there is often optic atrophy. The cerebellar component becomes more apparent with age. Evolving kyphoscoliosis and cardiomyo-pathy can cause cardiorespiratory compromise and death at 40-50 years
Ataxia telangiectasia
This disorder of DNA repair is an autosomal recessive condition. The gene (ATM) has been identified. There may be mild delay in motor development in infancy and oculomotor problems with incoordination and delay in ocular pursuit of objects (oculomotor dyspraxia), with difficulty with balance and coordination becoming evident at school age. There is subsequent deterioration, with a mixture of dystonia and cerebellar signs. Many children require a wheelchair for mobility in early adolescence. Telangiectasia develop in the conjunctiva , neck and shoulders from about 4 years of age. These children:
• have an increased susceptibility to infection, principally from an IgA surface antibody defect
• develop malignant disorders, principally acute lymphoblastic leukaemia (about 10%)
• have a raised serum alphafetoprotein
• have an increased white cell sensitivity to irradiation, which can be used diagnostically, but the ATM gene test is now mostly used.
Telangiectasia of the conjunctiva are present from about 4 years of age in ataxia telangiectasia.
Summary
• cerebellar is more common than posterior sensory pathway problems
• cerebellar causes - medication and drugs, varicella infection, posterior fossa lesions or tumours, genetic and degenerative disorders such as ataxic cerebral palsy, Friedreich's ataxia and ataxia-telangiectasia.
