Alien limb phenomenon (ALP) refers to the general behavior of an upper limb in performing autonomous complex movements against the patient's will. The various features include enabling synkinesis, intermanual conflict, grasping and groping, and utilization behavior. The common underlying feature is the complexity of movement and lack of voluntary control. Patients might show depersonalization towards the limb and criticize or rarely may even personify the limb. It is seen in lesions involving the frontal lobe, corpus callosum (anterior type), and less commonly, the parietal lobe (posterior type). Subcortical lesions producing the ALP are rare. We report a patient with a right-sided pontine hemorrhage with ALP.
A 48-year-old male patient presented with an acute onset slurring of speech as well as clumsiness, and numbness in the left half of body. He was hypertensive and on regular antihypertensive treatment and there was no other significant past or personal history. On evaluation, his blood pressure was 220/110 mmHg. His higher mental functions were normal. Cranial nerve examination showed right internuclear ophthalmoplegia, right lower motor neuron facial palsy (eight and a half syndrome), and impaired touch sensations over the left hemifacial region. His motor system examination was normal. Hemisensory loss (light touch, pain, temperature, vibration, and joint position sense) and cerebellar signs were noted in the left upper and lower limbs. On day three, he complained that his left upper limb would involuntarily approach his right while performing certain activities such as having food, removing a blanket, and brushing; there was no intermanual conflict. He noticed that his left upper limb would rise involuntarily and would also perform similar actions as his right upper limb. He was aware of these movements and expressed his inability to control them [Video 1]. These symptoms subsided in the next 1 week, while his cranial nerve and hemisensory symptoms persisted. His computed tomography and later magnetic resonance imaging brain showed hemorrhage in the right dorsal pontine tegmentum extending towards the midbrain without perilesional edema or mass effect [Figure 1].
Figure 1: (a-c) Right dorsal pontine tegmental hemorrhage extending toward the midbrain; (d-f) normal corpus callosum and cortex
In summary, our patient had acute onset cranial nerve palsies, left hemianesthesia and hemiataxia due to a right sided pontine hemorrhage. The structures involved were the right medial longitudinal fasciculus, facial colliculus and facial nerve (eight and a half syndrome), sensory nucleus of trigeminal nerve (hemifacial sensory loss), spinal and medial lemniscus (hemianesthesia, impaired vibration, and joint position sense in the left upper and left lower limb), and right cerebellar peduncle (left hemiataxia). During hospitalization, he noticed symptoms suggestive of an ALP in his left upper limb.
Feinberg initially classified ALP into the frontal and the callosal type. Posterior or sensory alien limb with accompanying sensory deficits is less commonly reported. In frontal alien limb, the lesion involves the left medial frontal lobe and corpus callosum. Anterior cerebral artery infarction and aneurysms are common etiologies. The clinical features include reflex grasping, groping, and compulsive tool manipulation by the dominant right hand. Callosal alien limb is seen in lesions involving the corpus callosum with or without bilateral or right frontal lesions due to anterior cerebral artery infarctions, aneurysms, tumors, and surgical resections in epilepsy. The nondominant hand is involved in these patients and shows a predominantly intermanual conflict. The parietal or sensory alien hand syndrome presents with parietal sensory deficits and hemineglect. The posterior cerebral artery infarction is a common cause. ALP is also seen as a part of neurodegenerative disorders like Alzheimer's disease and corticobasal ganglion degeneration.
Subcortical lesions producing an ALP are rare. There has been only one case report by Rafiei and Chang of a patient who developed the alien limb symptoms in the presence of left pontine hemorrhage. The authors hypothesized that a strategically placed lesion which interrupts both the cortically derived pathway and the left medial lemniscus might result in right sensory ALP. Our patient had alien limb features in his left upper limb in the form of left arm levitation, enabling synkinesis and mirror movements. The goal-directed nature and lack of voluntary control differentiated these movements from well-defined movement disorders. There were no grasping or groping movements, or intermanual conflict, as commonly seen with the anterior alien limb syndrome.
The pathogenesis of alien limb syndrome in pontine hemorrhage is uncertain. As with the posterior type, it may be related to changes in the body schema associated with lack of sensory feedback. The reticular nuclei in pontine tegmentum receive multiple sensory inputs from the spinal cord, cranial nerves, and cerebellum, which in turn project to the thalamus, hypothalamus, basal ganglia, and limbic system. These diencephalon structures have efferent connections with the frontoparietal regions. These complex pathways play an important role in the integration of sensory information and provide information regarding the body schema. The rarity of this condition and its transient nature prevents its better characterization compared to the common cortical variants.
I acknowledge Suryanarayana Sharma, Madhusudhan BK, Kiran Buddaraju, and Abhinandan KS for their valuable support in the preparation of this manuscript.