AHP was originally identified to be the “failure to identify an upper limb as one’s own on palpating it behind the back or with eyes closed” [4]. Thereafter, the definition was added to include one limb having unintended motor activity. AHP comprises at least two essential components: the dissociation of intention and the presence of semipurposeful or pseudovolitional movement. Some patients also show nonrecognition of the limb [3, 7]. Some definitions put emphasis on the automotor component, i.e., the dissociation between the individual’s intention and action, and that the action of the limb is driven by somebody else [1, 8]. Dood and Jankovic [2] have proposed a new definition: “AHP includes failure to recognize ownership of one’s limb, a feeling that one body part is foreign, personification of the affected body part, and autonomous activity which is perceived and outside voluntary control.”
Recently, the AHP has been divided into two types: the anterior and the posterior AHP. The anterior AHP includes the frontal type associated with reflexive grasping, groping and the compulsive manipulation of tools, and the callosal type characterized by intermanual conflict and the absence of frontal features. The posterior AHP is associated with prominent estrangement from the limb, rigidity, apraxia, cortical sensory findings and neglect [2, 9].
From the nosological perspective, Aboitiz [10] classified AHP into the following five classes: (1) diagonistic dyspraxia and intermanual conflict; (2) alien hand signs; (3) syndrome of the anarchic hand or way-ward hand; (4) supernumerary hands; and (5) agonisttic dypraxia.
In this report, all the three cases of AHP had no signs of auto-motor, therefore they belonged to the posterior type [9], or the second class of Aboitiz classification [10]. The case 3 experienced AHP immediately after ictals, which may be attributed to the Todd’s paralysis.
Since the 1990s, nine cases have been reported with AHP. Eight of them had seizure onset area in the right hemisphere, and one case had seizure onset area in the left hemisphere. Here, two of the three cases had seizure onset area in the left hemisphere, while one case in the right. All together, these 12 cases could be classified into the following types:
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(1)
Paroxysmal AHP, followed by ipsilateral upper limb convulsion. Three cases, including cases 1 and 4 in Leiguarda’s report [1], and the case in Brázdil’s report [5];
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(2)
Paroxysmal AHP followed by ipsilateral upper limb convulsion and then GTCS. Three cases, including case 2 in Leiguarda’s report [1], one case in Feinberg’s and our reports, respectively;
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(3)
Partial or generalized convulsion followed by AHP. One case, i.e., case 2 in our report;
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(4)
AHP associated with automatism. Three cases, including case 3 in Leiguarda’s report [1], and cases 1 and 2 in Boecebeck’s report [10];
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(5)
Initial partial seizures, followed by AHP after partial seizure remission. One case, i.e., the case in Kim’s report [8];
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(6)
Generalized convulsion immediately followed by AHP. One case, i.e., case 3 in our report.
The location of AHP has been identified in the supplementary motor area, the anterior cingulate gyrus, the anterior corpus callosum or the callosal genu, the posterior primary sensory cortex, the tertiary somatosensory cortex in the superior parietal lobule and the posterior postcentral gyrus [3, 5, 6]. The involvement of the occipital lobe and thalamus are rarely reported [6, 9, 11]. Unfortunately, no studies have addressed the onset zone of epileptic AHP episode.
The mechanisms of AHP have been reported in studies on non-epileptic diseases. The hypothetic mechanisms are as follows:
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(1)
SMA is involved in motor planning and initiation, as well as inhibition [6], and in the control and execution of internally generated motor sequences [1]. On the other hand, the inferior parietal lobule is a multi-model association area that contributes to and modulates the origin of other motor systems [1]. Dysfunction of the two areas may be the basis of AHP [1].
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(2)
The AHP is characterized by the coexistence of automotor activity and partial asomatogenosis [1]. This may be explained by the functional dissociation of the primary and supplemental association areas and simultaneous inhibition of the primary sensory cortex and primary motor cortex [7], simultaneous activation and inhibition of two or more cortical areas, as well as functional disassociation of the primary sensory cortex (S1) and supplementary sensory area (S2) [3, 10].
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(3)
If AHP is caused by a callosal lesion, the abnormal auto-motor activity would be dissociated from conscious volition due to the interhemispheric disconnection [1].
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(4)
The interhemispheric disconnection hypothesis. The corpus callosum connects both hemispheres and relays information between them. In a healthy subject, one hemisphere controls the activity of the contralateral limb, while simultaneously suppressing the contralateral hemisphere through corpus callosal connections. Damage to the connections can result in unwanted motor activity of the limbs. Damage to the function of the posterior region may result in a variant of a neglect syndrome (e.g. the loss of sense of ownership of the limb) [6].
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(5)
Resting-state fMRI findings. Ridley [12] reported a patient with developmental diagonistic dyspraxia (DD) during status epilepticus, which resolved over 2 years. Comparison of the whole-brain functional connectivity during acute DD with that after remission revealed that during the period of acute DD, the efficiency of salience and the right fronto-parietal networks were impaired, involving the frontal superior and midline structures, while after remission the network changes resolved.
In conclusion, the mechanism underlying AHP, particularly the rare epileptic paroxymal AHP, is poorly understood [4]. AHP can be represented before or immediately after convulsion, or be represented by the paroxysmal symptom only.
