Letter to the Editor: Confounding and Misclassification Obscures the Association Between Spinal Manipulation and Spontaneous Intracranial Hypotension

We read the Fernando et al study with interest, which presented a case and synthesized others of spontaneous intracranial hypotension (SIH) temporally related to spinal manipulative therapy (SMT). The authors proposed SMT is an underrecognized etiology of SIH related to dural tearing and cerebrospinal fluid (CSF) leakage. ¹ As it is important for chiropractors to examine potential adverse effects of SMT, we provide suggestions for authors to improve reporting of such cases, and propose a research design to clarify this topic.

Symptoms that prompted patients to seek chiropractic/SMT were not reported in 6 of 13 cases. The authors’ case could likewise be improved by describing these symptoms. Symptoms of SIH include those for which patients may seek SMT (i.e., protopathic bias), such as neck pain and/or stiffness, and headache. ² Such symptoms were noted in the remaining 7 of 13 cases (Jeret, Lin, Mathews, Morelli, Prasad, Strauss, and Suh et al). Either a lack of reporting or potential SIH symptoms in each included case suggests the authors’ conclusion of SMT being causative could be confounded by already-progressing SIH.

The authors’ attempt to exclude patients with connective tissue disease (CTD) was limited by unavailable testing, which could introduce misclassification bias. No cases described if necessary CTD screening was performed (e.g., Beighton score, skin examination, genetic panel). Comprehensive screening, ideally by a geneticist, should be performed to rule out CTD in all patients with spontaneous CSF leaks. ³ Also, the Strauss et al patient may have actually had CTD given her spinal meningeal diverticula, which predispose to dural tears. ²

Providers lacking extensive training for administering SMT were misclassified as “chiropractors.” The provider in Beck et al was a Heilpraktiker, ⁴ in Strauss et al an orthopedist, and in Lin et al may have been a massage therapist given treatment included pressing with the elbows and fingertips, and using a “massage bed.” Considering the lack of legal regulation of chiropractic in the Philippines, the authors should clarify if the treating provider in their case was a licensed chiropractor or other provider (e.g., massage therapist). ⁵ These providers could also be less likely to evaluate patients for appropriateness of SMT, considering possible SIH-in progress.

We hypothesize from the authors’ synthesis: (1) patients were treated using a non-recommended form of SMT, potentially not by a chiropractor, or (2) the observed relationship resulted from confounders such as SIH in-progress or concomitant CTD.

A case-control study could identify whether chiropractic SMT is a risk factor for SIH. A large population would be needed to query for SIH, CSF leak, or dural tears, given their rarity. Comparison of preceding chiropractic cervical SMT with primary care provider visits (SMT not usually performed) would account for protopathic bias and allow calculation of a measure of association.

Reporting patient’s symptoms prompting SMT, CTD screening findings, and correct use of “chiropractic” is vital to investigating the suspected relationship between SIH and SMT. Evidence from an epidemiologic study accounting for confounders would be required to determine if properly applied SMT is a risk factor for SIH.