A total of 196 patients were included in the study, 57 (29.1%) reported chronic pain. Patients’ median age was 41.1 years. Men constituted 82.6% of the study population, with 41 subjects (20.9%) having contracted HIV through heterosexual contact, 90 (45.9%) through homosexual contact, and 37 (18.9%) through the use of intravenous drugs. The subjects who had contracted HIV in a different way constituted 4.1%, and those who contracted the infection via an unknown route constituted 10.2% of the study population. All patients included in the study had been under specialist care at the HIV Outpatient Clinic of the Hospital for Infectious Disease in Warsaw, Poland at the time of enrollment. The individual subjects were included in the study in the order they presented at their infectious disease specialist’s office. Table 1 shows detailed patients’ characteristics.
Experiencing pain in the week prior to study inclusion was reported by 96 subjects (48.9% of the study group). The mean duration of pain was characterized as “several seconds” by 3 subjects (3.1%), “several minutes” by 28 subjects (28.9%), “several hours” by 51 subjects (52.6%), whereas “continuous pain” was reported by 13 subjects (13.4%). Out of the subjects reporting pain, 57 (59.4%) identified the onset of symptoms as over 6 months before study enrollment.
Location of chronic pain (n=57)
The part of the body most commonly reported to be affected by chronic pain were the lower limbs (24 subjects; 42.1%), followed by the upper limbs (15 subjects; 26.3%), back and lumbosacral region (13 subjects; 22.8%), head (11 subjects; 19.3%), abdomen (8 subjects; 14.0%), chest (4 subjects; 7.0%), and other regions (3 subjects; 5.3%). Generalized pain was reported by 3 subjects (4.3%). Forty-three subjects (75.4%) reported pain limited to a single region of the body, 12 subjects (21%) reported pain limited to two regions, and 2 subjects (3.5%) reported pain limited to 4 regions.
Pain intensity score in a Numerical Rating Scale
The subjects who declared chronic pain (n=57) rated pain intensity in a numerical rating scale (NRS). According to the established standard for this scale, the score of 1–4 points indicated mild pain, 5–6 points indicated moderate pain, and 7–10 points indicated severe pain. Assessed over the period of the previous 24 hours, the intensity of pain was rated as mild, moderate, or severe by 19 (33.3%), 24 (42.1%), and 14 (24.6%) subjects, respectively, when assessing their pain at its worst; by 47 (82.5%), 7 (12.3%), and 3 (4.2%) subjects, respectively, when assessing their pain at its least; and by 44 (77.2%), 7 (12.3%), and 6 (10.5%) subjects, respectively, when assessing their pain on the average. At the time of completing the questionnaire, 48 subjects (85.7%) rated their pain as mild, 4 subjects (7.1%) – as moderate, and 4 subjects (7.1%) – as severe.
Comparison of patient characteristics between the chronic pain group (n=57) and no chronic pain group (n=139).
Both study groups were statistically comparable with respect to sex (22.8% of women in the chronic pain group vs. 15.1% in the no chronic pain group; p=0.216), the presence of anti-HCV antibodies (28.0% vs. 17.3%, respectively; p=0.214), total HBcAb titers (24.6% vs. 24.5%; p=0.962), positive Venereal Disease Research Laboratory (VDRL) test (14.0% vs. 15.8%; p=0.509), the use of psychoactive drugs over the evaluated period (8.8% vs. 5.5%; p=0.519).
The median lymphocyte counts at the time when the subjects started to receive specialist care and at the study inclusion were also comparable between the two groups. In the group of those reporting pain, the median CD4+ cell count at the time when they started receiving specialist care was 348 cells/mcL (vs. 350 cells/mcL in the no-pain group; p=0.761), with 25% of the pain-reporting subjects having CD4+ counts lower than 189 cells/mcL (vs. <196 cells/mcL in the no-pain group). The most recent (prior to study inclusion) median CD4+ cell counts were higher at 516 cells/mcL and 563 cells/mcL, respectively (p=0.256).
At study inclusion, 184 subjects were receiving ART (55 in the pain group and 127 in the no pain group). The two groups were comparable in terms of ART rates (98.2% vs. 92.1%, respectively; p=0.185) and initial viral suppression (98.2% vs. 99.2%; p=0.517). Poor cART adherence (based on an initial questionnaire) was reported by 38.2% of subjects with chronic pain and by 30% of those without chronic pain (p=0.306).
The two groups differed significantly in terms of age at study inclusion (with the median age of 45.3 years in the pain group vs. 39.6 years in the no pain group; p=0.0002); median duration of specialist care (10.8 years vs. 4.9 years, respectively; p=0.0008), median nadir CD4+ cell counts (168 cells/mcL vs. 253 cells/mcL), median duration of ART (8.5 years vs. 3.4 years; p=0.0046), viral rebound after complete suppression (5.1% vs. 38.3%; p=0.018), as well as previous treatment with zidovudine (44.6% vs. 30.5%; p=0.063) and ‘D’ drugs (33.9% vs. 11%; p=0.0004) (Table 2).
The two groups also differed significantly in terms of the route of HIV infection. The chronic pain group was characterized by higher rates of individuals who contracted HIV through intravenous drug use (28.1% vs. 15.1%), heterosexual contact (21.0% vs. 14.8%), and in other ways (8.8% vs. 2.2%); whereas the no chronic pain group was characterized by higher rates of individuals who contracted HIV through homosexual contact (36.7% vs. 31.6%). The route of infection was characterized as unknown by comparable proportions of subjects from both groups .
Logistic regression analysis of factors associated with chronic pain
Univariate analyses showed that the epidemiological factors associated with the development of chronic pain were: the route of HIV infection, age at study inclusion, and specialist care duration (in years). The odds of developing chronic pain increased by 36% with each 5-year increase in the age of subjects at study inclusion and by 8% with each 10-year increment in the duration of specialist care. Analysis of the routes of HIV infection yielded a statistically significant result when the intravenous drug use (IDU) route was adopted as reference, and the p-value for effect was 0.0307. Compared with the IDU subgroup, the subgroups infected through the heterosexual, homosexual, and unknown routes showed lower chances of developing chronic pain. However, statistical significance was demonstrated only while comparing the homosexual and IDU routes, with the subjects infected through homosexual contact showing a 67% lower risk of developing chronic pain in comparison with those infected through IDU. The subgroup that reported HIV infection through a different route showed significantly (over two-fold) higher risk of developing chronic pain in comparison with the IDU subgroup. Table 3.
Ultimately, 184 subjects were included in the multivariate regression model. Those subjects who were not receiving any ART at the time of inclusion into the study were excluded from this analysis due to the fact that various aspects of ART were to be analyzed in this model. After adjustment for all factors significant in univariate analyses the only factors significantly associated with chonic pain was age. The odds ratio per 5-year increase in age was OR=1.28, with the 95%CI of 1.06–1.55 (p=0.0089). This means that when comparing two individuals with the same baseline characteristics (i.e. sex, route of HIV infection, nadir CD4+ cell count, specialist care duration (years), ART duration (years), previous use of AZT and ‘D’ drugs, and ART adherence (based on the presence or absence of viral rebound following complete suppression), the 5 years older individual had a 28% higher chance of developing chronic pain. From an individual perspective, this result indicated that with each 5-year increase in the patient’s age the risk of developing chronic pain was higher by 28%.