The Hoover sign and the trunk–thigh sign of Babinski are helpful in distinguishing hysterical from organic hemiplegia. The Hoover test is undertaken in the recumbent patient and is based on the downward pressure of one leg that is required to forcefully lift the opposite one. By placing the examiner’s hand under the heel of the unaffected leg, the sign is elicited when there is an absence of downward pressure as the patient attempts to raise the weak leg, thereby indicating a lack of voluntary effort. A second version of this test, also attributed to Hoover, is to detect downward pressure from the ostensibly paralyzed leg, as the good leg is raised. In a similar maneuver, the examiner tells the patient that he is testing the normal limb, while asking the patient to try to push the knees together. In hysterical weakness, the paralyzed limb adducts with normal power. One can take advantage of midline motor actions in the upper extremity by asking the patient to push his hands together and telling him that the normal side is being tested. In hysterical weakness, there is adduction movement of the supposedly paralyzed limb.
To carry out the Babinski trunk–thigh test, the examiner asks the recumbent patient to sit up while keeping his arms crossed in front of his chest. In the patient with organic hemiplegia from an upper motor neuron lesion, there is an involuntary flexion of the paretic lower limb; in organic paraplegia, both limbs are flexed as the trunk is flexed. In contrast, in hysterical hemiplegia, only the normal leg may be flexed; and in hysterical paraplegia, neither leg is flexed. Patients with apparently paralyzed legs who are seated in a rolling chair may propel themselves by pedaling along the floor (a sign attributed to Blocq by Okun and colleagues).
A discussion of motor paralysis would be incomplete without some reference to diseases in which muscle weakness may be profound but there are no overt structural changes in motor nerve cells or nerve fibers. Almost any disease of the neuromuscular junction and many diseases of muscle cause this combination. This group comprises myasthenia gravis, inflammatory myopathies, the muscular dystrophies, myotonia congenita (Thomsen disease), familial periodic paralysis, disorders of potassium, sodium, calcium, and magnesium metabolism, botulism, black widow spider bite, stiff-man syndrome, and the thyroid and other endocrine myopathies. In these diseases, each with a fairly distinctive clinical picture, the abnormality is essentially physiological or biochemical; their investigation requires EMG, special biochemical and histochemical tests, and electron microscopic study. These subjects are discussed in the sections on muscle disease later in this book.
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