Superficial abdominal reflex in syringomyelia: Associations with Chiari I malformation

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Highlights

  • In the largest cohort of patients studied to date with syrinx and evaluation for superficial abdominal reflex (SAR), we show that an abnormal SAR is more common in Chairi-associated syrinx, compared with idiopathic syrinx (P < 0.0001).

  • In our cohort of patients with idiopathic and Chiari-associated syrinx, the overall sensitivity of SAR for spinal cord syrinx was 48%.

  • After controlling for sex, age, syrinx size, syrinx location, scoliosis and presence of Chiari, the presence of Chiari was independently associated with an abnormal or absent SAR in patients with syrinx (OR 4.2, 95% CI 1.4–14, P < 0.01).

  • Patients with scoliosis were more likely to have an abnormal or absent SAR (P = 0.016).

  • These findings have implications for the pathophysiology of Chiari-associated and idiopathic syrinx and in the management of patients presenting with syrinx.

Abstract

An abnormal or absent superficial abdominal reflex (SAR) may be associated with an underlying spinal cord syrinx. The sensitivity of an abnormal or absent SAR and the relationship to Chiari malformation type I (CM-I) or syrinx morphology has not been studied. We aimed to describe the relationship between SAR abnormalities and syrinx size, location, and etiology. Children who underwent brain or c-spine MRI over 11 years were reviewed in this retrospective cohort study. Patients with idiopathic and CM-I–associated syringes (axial diameter ≥ 3 mm) were included. Clinical examination findings (including SAR) and imaging characteristics were analyzed. Of 271 patients with spinal cord syrinx, 200 had either CM-I–associated or idiopathic syrinx, and 128 of these patients had SAR-evaluation documentation. Forty-eight percent (62/128) had an abnormal or absent reflex. Abnormal/absent SAR was more common in patients with CM-I–associated syrinx (61%) compared with idiopathic syrinx (22%) (P < 0.0001). Abnormal/absent SAR was associated with wider syringes (P < 0.001), longer syringes (P < 0.05), and a more cranial location of the syrinx (P < 0.0001). Controlling for CM-I, scoliosis, age, sex, cranial extent of syrinx, and syrinx dimensions, CM-I was independently associated with abnormal or absent SAR (OR 4.2, 95% CI 1.4–14, P < 0.01). Finally, the sensitivity of SAR for identifying a patient with syrinx was 48.1%. An abnormal/absent SAR was present in most patients with CM-I–associated syrinx but in a minority of patients with idiopathic syrinx. This has implications for pathophysiology of CM-I–associated syrinx and in guiding clinical care of patients presenting with syrinx.

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.

Section snippets

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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