Superficial abdominal reflex in syringomyelia: Associations with Chiari I malformation

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.