Serum C-reactive protein levels in exfoliation syndrome and exfoliative glaucoma

Sir,

Exfoliation syndrome (XFS) is a systemic disorder of the extracellular matrix characterized by the accumulation of elastic microfibrils in which oxidative stress and a chronic low-grade inflammation is implicated in the pathogenesis.^{1, 2, 3} The purpose of this study was to evaluate the serum concentrations of CRP, a marker for systemic inflammation, in subjects with XFS and exfoliative glaucoma (XFG).

Case report

A total of 33 exfoliative subjects (14 subjects with XFG and 19 subjects with XFS) with a mean age of 69.5±11.6 years and 23 age-matched (mean age=67.3±10.5 years) control subjects were included in this study. A minimum sample size of 18 subjects was required to detect a clinically meaningful difference of 0.5 mg/dl with an alpha error of 0.05 and power of 0.90. Serum CRP levels were determined using nephelometric assay. The mean serum CRP level of subjects with exfoliation (0.54±0.46 mg/dl) (XFS+XFG combined) was not significantly different (P=0.274) than that of healthy subjects (0.42±0.28 mg/dl). In addition, the mean age, gender ratio, and serum CRP concentrations were similar between subjects with XFS, XFG, and controls (Table 1). Coronary artery disease and hypertension was present in 15.2% and 27.2% of exfoliative patients, respectively (Table 1).

Table 1. Clinical parameters and serum CRP concentrations in different groups included in the study.

Parameter	Group I (XFS) (n=19)	Group II (XFG) (n=14)	Group III (N) (n=23)	Test	P
Age (years)	69.4±13.3	69.8±9.3	67.3±10.5	ANOVA	0.449
Gender (F/M)	8/11	7/7	14/9	χ2	0.377
CRP (mg/dl)	0.53±0.38	0.55±0.57	0.42±0.28	ANOVA	0.549
CAD	2 (10.5%)	3 (21.4%)	1 (4.3%)	Fisher's exact test	0.308
HT	5 (26.3%)	7 (50.0%)	2 (8.7%)	Fisher's exact test	0.025

Abbreviations: CAD, coronary artery disease; CRP, C-reactive protein; HT, hypertension; N, normal; XFG, exfoliative glaucoma; XFS, exfoliation syndrome.

Comment

The interaction of co-pathogenetic mechanisms such as oxidative stress, tissue hypoxia, and release of growth factors (ie, TGF-β1) is believed to be associated with chronic low-grade inflammation and propensity to excessive inflammation following intraocular procedures associated with breakdown of the blood-aqueous barrier.^{1, 2} The presence of inflammation in XFS has been further substantiated by elevated aqueous interleukin-6 levels in early stages of XFS and the identification of C1q component of the complement system within the microfibrillar aggregates.^{3, 4} In addition, XFS has been shown to be correlated with age-related macular degeneration, another disorder with underlying inflammatory mechanisms in which serum CRP levels have been found to be elevated.⁵

Our results revealed that serum CRP levels were not elevated in patients with XFS and XFG. In a recent study, serum levels of CRP in XFS and XFG were found to be similar to that of healthy controls.⁶ In that study, all subjects with a history of vascular disease including hypertension and coronary artery disease were excluded; however, exclusion of subjects with vascular disease may potentially be representative of patients with a milder phenotypic disorder. Nonetheless, on the basis of our results and those of Yuksel et al,⁶ we suggest that XFS-associated inflammation is not able to induce hepatic synthesis of CRP and is associated with a limited local and subclinical inflammatory reaction in involved tissues.

The authors declare no conflict of interest.