Background Surgery is not a recognised potential amyotrophic lateral sclerosis (ALS) risk factor that might modify the onset or course of ALS.

Methods We studied our database of ALS patients, which includes questions concerning surgical procedures. We defined surgery as an operative procedure requiring general or regional anaesthesia, but not local anaesthesia. Patients were classified as G1—no surgery; G2—surgery performed ≥3 months before disease onset; G3—surgery <3 months before disease onset; and G4—surgery after disease onset. The ALS-FRS score was evaluated every 3 months from presentation. The maximal ALS-FRS score was ascribed to disease onset, itself defined as symptom onset.

Results 657 patients with ALS were studied. In G3 there was a positive correlation between onset-region and surgery-region (p=0.032). In G4, 35 (57.6%) patients had surgery, probably due to initial misdiagnosis. The rate of functional change (%) in G4 was significantly greater in the 3-month period immediately after surgery as compared with the 3-month period before (1.46%±1.35 vs 6.30%±8.10, p=0.005) and the following 3 months (3.30%±3.10, p=0.006).

Conclusions The site of surgery before ALS onset correlates with the region of onset of ALS. Patients with slower disease progression are at an increased risk of undergoing surgery, probably as part of initial difficulty in diagnosis. We noted accelerated disease progression during the 3-month period after surgery. Definite diagnosis is important to avoid unnecessary surgical trauma and subsequent more rapid deterioration.