Which neurologic findings are characteristic of Kennedy disease (KD)?

Updated: Sep 30, 2019
  • Author: Paul E Barkhaus, MD, FAAN, FAANEM; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

Cognition is unimpaired.

Examination of the cranial nerves usually shows evidence of weakness in the facial, palatal, and tongue muscles. (See images below.) The weakness may be so profound that the mouth hangs open and is tremulous. In the index case Kennedy et al reported, the facial weakness became so severe that the patient held his chin up with his hands to chew. Jaw drop may be a prominent feature. [50] Although eye movements are typically spared, there has been one case report of abnormal extra-ocular motility in KD. [12]

The forehead of this patient with Kennedy disease The forehead of this patient with Kennedy disease is smooth, in fact, too smooth for a man this age. The smoothness is particularly noticeable when the patient tries to perform upgaze, when wrinkling of the forehead due to contraction of the frontalis is expected.
Photographs show asymmetry at rest due to facial w Photographs show asymmetry at rest due to facial weakness, which is enhanced when the muscles are activated by pursing the lips.

Contraction of perioral musculature may elicit twitching movements of the chin (quivering-chin phenomenon). This also may be seen when the patient is at rest, ie, not activating his facial muscles.

The voice changes and may become nasal. The tongue usually shows scalloping (irregularity of the borders) or a deep furrowing in the midline as the bundles of muscle forming the glossal group become wasted and separate at the midline. Laryngospasm may occur. [51] (See image below.)

Note the scalloping of the borders of the tongue, Note the scalloping of the borders of the tongue, which strongly suggests wasting. In addition, the marked wasting of the large group of glossal muscles on each side has caused them to separate and form a midline furrow.

Although bulbar involvement usually follows limb involvement, it is occasionally the presenting weakness.

Muscle strength may show a classic pattern of proximal-greater-than-distal impairment, beginning in the legs. However, Ferrante and Wilbourn showed variation in distribution of initial weakness ranging from symmetry to asymmetry, from proximal to distal predominant weakness, and from upper extremity to lower extremity. [52]

In mild to moderately severe cases, prominence of bony landmarks should be sought to confirm wasting. If the patient is ambulatory, proximal weakness may cause a hyperlordotic standing posture and internally rotated arms, ie, simian stance, in which the thumbs point medially or toward the patient rather than straight forward (see image below).

Note wasting in the thighs and shoulders. The arms Note wasting in the thighs and shoulders. The arms hang down and are rotated internally so that the thumbs point toward the patient (ie, simian posture) rather than forward, as in a healthy individual. This observation strongly suggests weakness in shoulder girdle muscles.

Fasciculations, or spontaneous discharges of single motor units, are seen easily in affected musculature. The patient should be evaluated at complete rest in a warm environment. In particular, care should be taken not to mistake postural movements in the tongue for fasciculations.

In weak muscles, minimal isometric activation or contraction of muscle may result in large, coarse, and regular movement of a portion of the muscle that superficially may resemble a fasciculation. This is sometimes (and unfortunately) called contraction fasciculation. In normal muscle, isometric activation or contraction of muscle is not associated with what appears to be a coarse and jerking movement.

In patients with chronic denervation-reinnervation in whom motor units are markedly enlarged (ie, a single motor neuron innervates more than twice the number of muscle fibers), these appear as twitches associated with activation.

Although not to be confused with fasciculations per se, these clinical findings are important, as their presence indicates a chronic neurogenic process until proven otherwise.

The quivering-chin phenomenon, when seen with facial muscle activation, may be the result of the activation of the few enlarged motor units.

Muscle stretch responses are variable; they range from normal to depressed and are usually absent in the ankles. Generally, no upper motor neuron dysfunction occurs in KD; however, Pachatz et al show evidence for subclinical involvement using transcranial magnetic stimulation, [53] but this finding was not confirmed in a subsequent study. [14]

Sensation is often clinically normal to the modalities of vibration perception, position sense, sharp touch, and light touch, despite the demonstration of abnormalities in morphology and autonomic testing. [11, 54, 55, 56] If sensation is impaired, it is important to distinguish a pattern that might suggest a diabetic polyneuropathy.


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