Superficial abdominal reflex in syringomyelia: Associations with Chiari I malformation
Introduction
Syringomyelia, a cystic dilatation of the central canal within the spinal cord, may develop in association with cranio-cervical junction or spinal conditions such as Chiari malformation type I (CM-I), tethered cord, tumor, trauma, infection, and scoliosis. In the absence of any associated pathology, it is considered idiopathic. Clinically, a syrinx may be asymptomatic or associated with progressive pain, stiffness, weakness, and impairments in temperature and pain sensation. Identifying a spinal cord syrinx or any associated findings such as CM-I is clinically relevant as treatment may be warranted.
The superficial abdominal reflex (SAR)—also known as the umbilical reflex—is a diagnostic tool used to identify occult lesions in the neuraxis, particularly in the setting of an otherwise normal neurologic exam. Initially described in 1876 [1], subsequent EMG studies identified the SAR as a spinal reflex circuit that can be modulated by descending central pyramidal tracts [2], [3]. The SAR can be elicited by stroking each of the four quadrants of the abdomen around the umbilicus. A normal response is identified by visualizing contraction of the abdominal muscles on the ipsilateral side [4]. Abnormalities in the SAR—including an asymmetric, diminished, or absent SAR—have been noted to predict the presence of spinal cord syrinx in associated conditions, but have not been studied in a cohort with known spinal cord syrinx [3], [5], [6], [7], [8], [9], [10], [11].
Although the relationship of an asymmetric, diminished, or absent SAR with spinal cord syrinx has been described [3], [5], [6], [7], [8], [9], [10], [11], the sensitivity of the SAR for syrinx and the relationship of the SAR to syrinx etiology or morphology are unknown. We hypothesized that in patients with a known syrinx, the presence of an altered or absent SAR is associated with additional pathology such as CM-I. Therefore, this study aimed to determine the relationship between SAR and syrinx etiology and morphology, and the sensitivity of an abnormal SAR for syrinx, in the largest studied cohort with spinal cord syrinx and SAR evaluation.
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Materials and methods
This retrospective cohort study was approved by the Institutional Review Boards of the University of Michigan and Washington University in St. Louis. A database consisting of 14,118 consecutive patients 18 years or younger who underwent brain or spine MRI over 11 years at one tertiary referral center was reviewed to identify patients with spinal cord syrinx of any origin [12]. Electronic records were searched [13] for the following key words: “syrinx”, “syringomyelia”, and “hydromyelia”.
Patient population
Of the 14,118 individuals who underwent brain or spine MRI, 128 patients had either idiopathic or CM-I-associated syrinx as well as documentation of a SAR test. Thus, the base cohort consisted of these 128 patients. Table 1 details the demographic characteristics.
Abnormal superficial abdominal reflex
An abnormal SAR was defined as an asymmetric, diminished, or absent SAR. Among the 128 patients with spinal cord syrinx and documented SAR, 62 (48%) had an abnormal SAR. In 47 of these 62 patients (75.8%), the abnormal SAR was the only
Discussion
This study describes the association between the SAR and characteristics of spinal cord syrinx. We demonstrate that an abnormal SAR is associated with wider, longer, and more-cranially located syringes. CM-I–associated syringes are significantly larger in diameter and more frequently lead to an abnormal SAR than idiopathic syringes, though they are not significantly longer. Furthermore, those with syrinx and an abnormal SAR are significantly more likely to have scoliosis than those with a
Conclusions
An abnormal or absent SAR is more common in CM-I-associated syrinxes, and this relationship is independent of tonsil position or syrinx characteristics. As such, an abnormal SAR may guide further workup and the clinical management of spinal cord syrinx.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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