Prognostic value of phrenic nerve conduction study in amyotrophic lateral sclerosis: Systematic review and meta-analysis.

Silva, Cláudia S; Rodrigues, Filipe B; Duarte, Gonçalo S; Costa, João; de Carvalho, Mamede

OBJECTIVES To assess the prognostic value of phrenic nerve conduction (PNC) in amyotrophic lateral sclerosis (ALS). METHODS We conducted a systematic review to identify studies reporting on PNC, and mortality and/or forced vital capacity (FVC) in patients with ALS. We searched Medline, EMBASE, and Web of Science. Two independent authors selected studies and extracted data. Risk of bias was assessed using the QUIPS tool. Hazard-ratios and correlation coefficients were pooled using a random effects generic inverse-variance model. Evidence quality was evaluated with GRADE. RESULTS In the pooled analysis, patients with CMAP-amplitude equal or below 0.4 mV are 2.021 more likely to die over the studied period (95%CI 1.161-3.522; I2 = 55.9%; 338 participants). CMAP-amplitude showed a moderate positive correlation with FVC (r = 0.400, 95%CI = 0.226-0.550; I2 = 69.77%; 381 participants). However, there was a weak negative correlation between CMAP-latency and FVC (r = -0.235; 95%CI = -0.447 to -0.024; I2 = 15.92%; 112 participants). CONCLUSIONS There is moderate-quality evidence that CMAP-amplitude of the PNC is correlated with FVC. Results favour a predictive value for mortality, but the risk of bias is high. SIGNIFICANCE PNC is a simple test that should be considered to assess respiratory function in ALS, especially in patients with bulbar involvement or cognitive impairment.