3.2 Physical dependence and opioid withdrawal
In addition to tolerance and OIH, pain in patients with OUD can be complicated by the consequences of physical dependence, namely opioid withdrawal hyperalgesia89-91. Opioid withdrawal is commonly assessed using standardized scales such as the Clinical Opiate Withdrawal Scale (COWS)92, the Subjective Opioid Withdrawal Scale93, and the Objective Opioid Withdrawal Scale (OOWS)93. These tools evaluate self-reported symptoms and observer-rated signs of opioid withdrawal, including anxiety or irritability, perspiration or sweating, tearing or lacrimation, runny nose or rhinorrhea, goosebumps or piloerection, restlessness, as well as the presence of specific types of pain itself (e.g., abdominal pain and cramps).
However, there is considerable overlap between the symptoms of opioid withdrawal and those associated with poorly treated chronic pain. For example, feelings of irritability94, anxiety95, and restlessness96 can be associated with chronic pain as well as opioid withdrawal. This overlapping symptomatology makes it challenging to differentiate etiology, potentially leading to inadequately treated pain in clinical practice. Hence, clinicians must consider the possibility of undertreated pain when evaluating opioid withdrawal, especially in patients with known OUD. Figure 2 provides clinical pain assessment parameters to distinguish between opioid hyperalgesia, tolerance, and withdrawal. Such differential assessment can prevent premature diagnostic closures that negatively affect pain-related functioning.