Intermittent cancer pain: clinical importance and an updated cancer pain classification.

AIM: We report the characteristics of intermittent cancer pain. In addition, we propose a new clinically based classification.

METHODS: Consecutive patients with cancer referred to our palliative medicine service were consented and underwent a comprehensive pain evaluation including available laboratory and radiological studies, at the time of initial contact.

RESULTS AND DISCUSSION: In total, 100 consecutive patients reported 158 different pain sites. Pain temporal pattern observed was 60% of patients had continuous (CP) plus intermittent pain (IP); 29% IP alone; and 11% CP alone. The etiology of IP was somatic (58%), visceral (24%), neuropathic (7%), and mixed (11%). Median duration of IP was 4 months with a median daily frequency of 4 episodes. Consequently, we propose that IP be classified into IP alone or nonbreakthrough pain (NBP; because there is no underlying CP or around-the-clock [ATC] opioids used) and breakthrough pain (BP; because there is underlying CP or/and ATC opioids used). We propose that both BP and NBP be each subclassified into 3 categories: (1) incident, (2) non-incident, and (3) mixed. In addition, a 4th category exclusive to BP: end-of-dose failure. Incident pains made up (N = 42, 47%) nearly half of all IP. According to our classification, incident pain was part of BP in 41% (N = 25) or NBP in 58% (N = 17). Incident NBP received less treatment than incident BP, and it was less controlled.

CONCLUSION: (1) Intermittent pain is a major problem in patients with cancer, (2) NBP is a common but under-recognized form of cancer pain, (3) NBP is less defined and controlled than BP, (4) incident NBP accounts for 40% of all incident cancer pain, and (5) variable IP definitions and classifications make comparisons between studies difficult.