Alternating Syndromes

ALTERNATING SYNDROMES represent such a combination of neuropathological phenomena of functional loss, when one part is externally expressed on one half of the body (for example, in the form of right-sided paralysis or paresis of the extremities), and the other on the opposite (i.e., left) side of the face (for example, in the form of atrophic facial paralysis). Topically, the A. syndrome indicates damage to the stem part of the brain, i.e., the cerebral peduncle, Varolius' bridge, and medulla oblongata. Pathophysiologically, paralysis of the extremities is explained by the disruption of the integrity of the corticospinal (pyramidal) tract on the side opposite to the paralysis of the extremities; with paralysis of the left extremities, the focus of damage should be sought in the right half of the corresponding part of the brainstem, and vice versa. The corticospinal (pyramidal) tract makes a more or less complete decussation at the boundary between the medulla oblongata and spinal cord, consequently, the interruption of the tract above the decussation point causes the appearance of paralytic phenomena in the extremities of the opposite side. The presence of symptoms of damage to cranial nerves on the side opposite to the paralysis of the extremities in the A. syndrome is explained by the involvement in the disease of the nucleus or root of one nerve or another, located adjacent to the site of damage to the corticospinal tract. It is customary to distinguish A. syndromes with localization of the pathological process in the cerebral peduncle, pontine, and bulbar syndromes. With localization of the process in the cerebral peduncle, there may be: a) Weber's syndrome, b) Benedikt's syndrome, c) Foix's syndrome, d) Claude's syndrome. Weber's syndrome (Hemi-plegia alternans oculomotoria) is manifested by spastic paralysis (paresis) of the extremities, trunk, tongue, and face on one side, with paralysis of the oculomotor nerve on the other side. On autopsy, softening or hemorrhage is found in the area of the cerebral peduncle; sometimes the pathological process begins in the meninges (e.g., gumma) and spreads to the cerebral peduncle (see Fig. 1). Benedikt's syndrome is characterized by paralysis of the oculomotor nerve on one side and choreo-athetotic movements with tremor of the extremities on the opposite side, sometimes in the presence of hemianesthesia. The focus of damage in this syndrome also involves the red nucleus and cerebellar pathways. With foci in the area of the red nucleus, it is currently customary to distinguish two A. s: a) the superior red nucleus syndrome (Foix's syndrome), arising from isolated damage to the anterior part of the red nucleus and, partially, the thalamus and subthalamus, and b) the inferior red nucleus syndrome (Claude's syndrome) with simultaneous damage to the oculomotor nerve nucleus and the posterior pole of the red nucleus. Foix's syndrome is characterized by cerebellar phenomena, namely choreo-athetotic movements, sometimes intentional hemitremor, sensory disturbances, and changes in the visual field, without damage to the oculomotor nerve. Claude's syndrome manifests as paralysis of the oculomotor nerve on the side of the focus and cerebellar hemisyndrome (adiadochokinesia, dysmetria, etc.) on the other side; sometimes dysarthria and swallowing disorders occur. Both the superior and inferior red nucleus syndromes (according to Foix) develop when branches of the posterior cerebral artery (art. cerebri post.) supplying the red nucleus are damaged, namely the anterior, middle, and posterior arterioles of the red nucleus. Among the pontine syndromes, we can mention a) the anterior pontine syndrome of Millard-Gubler and Brissaud-Sicard, b) Foville's syndrome, and c) Raymond-Cestan's syndrome. Millard-Gubler's syndrome (Hemiplegia alternans facialis) is manifested by spastic paralysis of the extremities on one side and paralysis of the facial nerve on the other side; the facial paralysis is of peripheral type. The lesion site is usually located at the base of the pons (see Figure 2). Brissaud-Sicard's syndrome consists of spastic paralysis of the extremities on one side and facial spasm on the opposite side. Foville's syndrome is characterized by spastic paralysis of the extremities on one side and paralysis of the facial and abducens nerves on the opposite side; at the same time, so-called paralysis of gaze is often observed. The syndrome sometimes develops as a result of thrombosis of the a. basilaris. Raymond-Cestan's syndrome consists of coordination disorders, choreo-athetotic movements, sensory disturbances, hemiparesis on one side, and paralysis of conjugate movements in eye abduction on the opposite side. Bulbar alternating syndromes are divided into interolivary and retro-olivary. The interolivary bulbar syndrome, Jackson's syndrome (Hemiplegia alternans hypoglossica), is characterized by the presence of spastic paralysis of the extremities on one side and atrophic paralysis of the hypoglossal nerve on the opposite side. The syndrome often develops as a result of thrombosis of branches of the a. spinalis anter. (so-called arteriolae spino-bulbares Poccoclimo, see Figure 3). Among the retro-olivary syndromes, we can mention a) Avellis' syndrome and b) Babinski-Nageotte's syndrome. Avellis' syndrome consists of paralysis of the extremities on one side and paralysis of the soft palate and vocal cord on the other side; sometimes there is hemianesthesia; paralysis of half of the soft palate and vocal cord is associated with damage to the nuclei ambiguus. In Babinski-Nageotte's syndrome, hemiparesis and hemianesthesia are observed on one side, and cerebellar symptoms on the other: hemiasynergy, lateropulsion, and nystagmus. It occurs in thromboses of branches of the a. vertebralis, e.g., a. cerebelli infer. post. Other types of A. syndromes are possible depending on damage to various nerves of the stem part; the specific feature of the A. syndrome will always be paralysis of a cranial nerve on the side of the focus and spastic or sensory paralysis on the opposite side; for example, so-called hemianesthesia alternans (Raymond) may occur, in which there will be hemianesthesia on one side of the body, and anesthesia of the face will develop on the opposite side; for this, it is sufficient if the focus involves the nucleus or root of the trigeminal nerve and the main lemniscus. Hemianesthesia alternans develops as a result of thrombosis of art. cerebelli infer. post, and arteriae lateralis bulbi; the basins of these arteries occupy the retro-olivary areas of the brainstem, along which the tractus spino-thalamicus (conducting pain and thermal sensations) passes; therefore, with obstructions in this area, anesthesia of the trigeminal nerve on the same side is joined on the opposite side by dissociated anesthesia in the form of thermanalgesia.

Paralysis from occlusion of these arterial twigs usually forms without loss of consciousness, with paralysis of the soft palate, vocal cord, and trigeminal nerve developing on the affected side, as well as Horner's symptom complex (Claude Bernard) and disturbance of swallowing; according to Zakharchenko, cases of embolism of art. cerebel. infer, poster. are great rarities. In thrombosis of spinobulbar arterioles, branches (according to Rossolimo) of the anterior spinal artery, which feed the pyramids, - so-called crossed hemiplegia (hemiplegia cruciata) may develop in the form of paralysis of the arm on one side and paralysis of the leg on the other; in this case, part of one 'pyramid' is damaged above, and part of the other - below the crossing of the corticospinal tract.