THE PLANTAR REFLEX - RePub

ilateral operations). Adding this to the less startling fact that normal
plantar responses were found in other patients who eventually showed
severe descending degeneration of the lateral tracts (I shall discuss this
problem separately), the authors arrived at the iconoclastic conclusion:
'any lesion of the lateral and ventral columns of the cord may, or may not,
cause the Babinski response'.
However, the question of Babinski signs in the absence of obvious
corticospinal degeneration is only a pseudo-problem, as Walshe (1956)
was quick to point out. The fallacy is to assume that a non-degenerated
pyramidal tract is the same thing as a normal pyramidal tract, particularly
for patients in whom a cordotomy lesion borders upon pyramidal fibres:
focal demyelination can produce severe loss of function without Wallerian
degeneration. The experimental demonstration of conduction block by
focal demyelination in the central nervous system is only a recent
milestone in neurology (McDonald and Sears, 1970).
From the clinico-pathological side, however, it had been noted long
before that demyelinating lesions with preservation of axis cylinders could
produce neurological deficits, and Babinski was also a pioneer in this
particular field (Babinski, 1885), together with Holmes (1906). It is
therefore hardly surprising that he described patients with the toe
phenomenon in whom the pyramidal tracts were not degenerated
(Babinski, 1898, 1899 a, 1911 a). Nathan and Smith (1955) comment that
Babinski, by these lines, disproved his own supposition about the relation
between pyramidal tract and upgoing toe sign; this interpretation is
inappropriate, as Babinski was very much alive to the relative importance
of absent secondary degeneration - some of his cases were paraplegic!
Walshe (1956) also gives Babinski too little credit in this respect, although
the latter was not always fully consistent in that he sometimes explained
an absent toe phenomenon by referring to undegenerated lateral tracts
(Babinski, 1906 b, 1911 a).
In summary, the evidence that Babinski signs can result from lesions
outside the pyramidal tract rests on incorrect premises. But of course this is
a negative conclusion which does not prove the reverse.
'Pure' pyramidal lesions
Anatomical evidence from lesions caused by disease is often ambiguous,
not only because absence of secondary degeneration does not necessarily
imply functional integrity, but also because most lesions interfere with
more than one fibre system. For this reason a number of studies were
wholly or partially devoted to the plantar reflex after experimental lesions
in monkeys and apes.
113