The differentiation among the childhood ataxias is difficult. The problem is twofold—first, to be certain that ataxia exists and, second, to differentiate cerebellar ataxia from the sensory ataxia of peripheral nerve disease and from generalized tremor and polymyoclonus. Because cerebellar ataxia is more a disorder of voluntary than of postural movements, its presence usually cannot be determined with certainty until intentional (projected) movements become part of the child’s repertoire of motor activity. As indicated in Chap. 27, the earliest signs become manifest in the arms when the infant reaches for an object and brings it to his mouth or transfers it from hand to hand. A jerky, wavering, tremulous movement then appears; in sitting, titubation of the head and a tremor of the trunk may be apparent. Once walking begins, apart from the usual clumsiness of the toddler, there is a similar incoordination of movement. Sensory ataxia is always difficult to distinguish but is rare at this age and usually accompanied by weakness and absence of tendon reflexes. By the fourth or fifth year, when more detailed sensory testing becomes possible, the presence or absence of a proprioceptive disturbance and a Romberg sign can be demonstrated.
The group of persistent and progressive cerebellar ataxias is heterogeneous and of varied etiology; some of them merge with Friedreich ataxia, Levy-Roussy neuropathy, and other adolescent–adult degenerative hereditary ataxias. These disorders are discussed in Chap. 38. There are many other childhood ataxias that probably belong in the category of degenerative disease, some in which cerebellar ataxia is the most prominent disorder and in which other neurologic abnormalities are more prominent. To describe each in detail would be impractical in a book on the principles of neurology; consequently, the non-
Friedreich ataxias are only tabulated here.
1. Cerebellar ataxia with diplegia, hypotonia, and mental retardation (also called atonic diplegia of Foerster); this is a form of cerebral palsy.
2. Agenesis of the cerebellum: early cerebellar ataxia (with or without mental retardation) and episodic hyperventilation; this group included the selective agenesis of the vermis—Joubert syndrome.
3. Cerebellar ataxia with cataracts and oligophrenia: onset from childhood (mainly) to as late as adult years (Marinesco-Sjögren disease).
4. Familial cerebellar ataxia and retinal degeneration (Behr disease).
5. Familial cerebellar ataxia with cataracts and ophthalmoplegia or with cataracts and mental as well as physical retardation.
6. Familial cerebellar ataxia with mydriasis.
7. Familial cerebellar ataxia with deafness and blindness and a similar combination, called retinocochleodentate degeneration, involving the loss of neurons in these three structures.
8. Familial cerebellar ataxia with choreoathetosis, corticospinal tract signs, and mental and motor retardation.
In none of the syndromes mentioned above has a biochemical abnormality been established, so their metabolic nature is a matter of speculation. However, disorders of the electron transport chain can, on occasion, present as the Marinesco-Sjögren phenotype, mentioned above.
The persistent cerebellar ataxias of childhood in which a metabolic fault or mutation has been demonstrated are as follows: 1. Refsum disease 2. Abetalipoproteinemia (Bassen-Kornzweig syndrome) 3. Ataxia-telangiectasia (see Chap. 37) 4. Galactosemia 5. Friedreich ataxia
Bassen-Kornzweig syndrome (onset more often in late than in early childhood) is described in the following section of this chapter. Ataxia-telangiectasia is described below.