A study published ahead-of-print by the journal Spine suggests that smoking may have a directly toxic effect on the healing capability of the spinal cord, particularly if the patient in questions is a heavy smoker.
Cigarette smoke contains at least 3,500 identified compounds, the most important of which are nicotine and carcinogenic polycyclic aromatic hydrocarbons. The study authors, led by David J Kusin, Case Western Reserve University School of Medicine, Cleveland, USA, note that “It is well established that nicotine is a potent vasoconstrictor”, and that “nicotine alone in the absence of cigarette smoke can inhibit neovascularisation in animal models”. Given these and the “many other” negative effects of smoking, it “is reasonable to assume that smoking has a negative influence on outcomes of cervical spondylotic myelopathy (CSM) surgery”. This study is the first to investigate on functional outcomes of CSM surgery as measured by the Nurick score.
The retrospective cohort study compared outcomes of surgical treatment of cervical myelopathy between smokers and non-smokers as assessed by the Nurick score. Kusin and colleagues write that although the harmful effects of smoking on healing have been well established, the effect of smoking specifically on postoperative outcomes for cervical myelopathy has not been specifically evaluated.
The medical records of 212 patients who underwent surgery for CSM were reviewed by the study team. Inclusion criteria were the diagnosis of CSM with a Nurick score, surgical intervention, and at least two years’ follow up. The patients were categorised into two groups according to smoking status and stratified according to cigarette pack years and cigarette packs per day—measures of long-term tobacco exposure. CSM was identified by the presence of upper motor signs, clonus, gait abnormalities, or difficulty with fine motor movements such as buttoning a shirt.
Age at presentation, sex, preoperative and postoperative Nurick score, duration of symptoms preoperatively, duration of follow up, procedure performed, surgical approach, number of levels fused, diabetes status, cocaine use, ethanol use, preoperative MRI signal change, and whether the patient belonged to Veterans Affairs were recorded. Analysis was conducted using simple linear regression and multiple regression. Patients were evaluated postoperatively at six weeks, three months, six months, one year, and annually thereafter.
Kusin et al report that univariate analysis demonstrated a postoperative improvement in non-smokers of 1.53 points on the Nurick scale compared to 0.6 points in the smoking group (p<0.001). There was also a “clear negative association between packs per day and change in Nurick score” (p<0.0001) and “negative association between pack years and change in Nurick score” (p<0.0001). The authors note that there was a greater improvement in Nurick score with greater (worse) preoperative score, but only in patients with fewer than 25 pack years. Smoking status was not associated with preoperative Nurick score.
Smoking status was not found to have an effect on preoperative Nurick score, suggesting that “there is a threshold of tobacco induced insult to the spinal cord beyond which the ability of the cord to recover is quantified,” the authors write. “This threshold of exposure seems to be greatly decreased in patients who already have significant spinal cord injury”.
Kusin and colleagues thus conclude that “smokers are associated with a poor improvement in Nurick score following surgical treatment of cervical myelopathy. Smoking may have a directly toxic effect on the intrinsic healing capability of the spinal cord, particularly beyond 25 pack years.”