Department of Rheumatology, University Hospital Aintree, Liverpool, UK
Correspondence to: S. Busteed, Arrowe Park Hospital, Arrowe Park Rd., Upton, Wirral, CH49 5PE. E-mail: sandra_busteed{at}hotmail.com
SIR, We read with interest the recent paper by Mukerjee and colleagues [1] on the use of non-invasive screening methods for pulmonary arterial hypertension (PAH) in systemic sclerosis (SSc). The authors conclude that while echocardiography and pulmonary function testing have good positive predictive accuracy in cases of advanced PAH, non-invasive techniques are not sensitive or specific enough to exclude early PAH in SSc. At our unit, we recently conducted a case note review on patients with SSc to audit screening practices for PAH in line with current recommendations. The screening guidelines issued by our local pulmonary vascular disease unit in Sheffield advise referral (i) if patients have a tricuspid gradient (TG) of between 30 and 40 mmHg and are breathless or have a DLCO (diffusing capacity for carbon monoxide) of less than 50%, and (ii) in all patients with a TG greater than 40 mmHg, regardless of symptoms or DLCO. Further investigations are recommended for patients with unexplained dyspnoea.
A few points of note emerged from this review. In total, 18/53 patients (34%) did not have a recordable TG on one or more echos due to absent tricuspid regurgitation. This figure is comparable with other studies [2]. Of 53 who underwent pulmonary function testing, 15 had at least one DLCO reading <50% and three of these 15 patients did not have a recorded pulmonary artery pressure. All three of these patients did have underlying lung disease, however. A further three patients who were found to have a raised TG (>40 mmHg) on echocardiography had a previous echo showing no evidence of tricuspid regurgitation. One patient had a DLCO of 48% with exertional dyspnoea and a normal high-resolution CT of the thorax; however, a TG was unrecordable since 1998. Overall, of the 48 patients currently attending our unit, 14 met referral guidelines for a pulmonary vascular disease unit (29%). Two of these patients had only marginally elevated pulmonary artery pressures and had underlying reasons for their dyspnoea (chronic obstructive pulmonary disease and chronic renal failure). Seven of the 14 had evidence of interstitial lung disease on high-resolution CT of the thorax.
With the development of pulmonary vascular disease units and the availability of drugs like bosentan, it is imperative that screening for PAH is carried out in SSc with referral as appropriate. Screening guidelines have limitations, however, in that low threshold values may give rise to a large number of tertiary referrals. It is not known if asymptomatic SSc patients with a mild elevation in the sPAP (Systolic Pulmonary Artery Pressure) will go on to develop significant PAH [3]. However, as demonstrated in Mukerjee's study, higher thresholds will result in cases of PAH being missed. In their cohort of 137 patients, 33 were found to have PAH on catheterization with only a modestly elevated TG (<35 mmHg) on echocardiography (seven with lung fibrosis and 26 with idiopathic PAH).
In general, a significant proportion of patients do not have a measurable sPAP because of absent tricuspid regurgitation and some of these patients have evidence of raised pulmonary artery pressures on repeat echocardiography. This may be particularly relevant in patients with a low or declining DLCO. A Japanese study of patients with scleroderma and mixed connective tissue disease found that 3/12 patients without measurable TR (Tricuspid Regurgitation) had evidence of PAH on cardiac catheterization [4]. Although patients with SSc develop dyspnoea at relatively low pulmonary artery pressures, the issue may be further complicated by the incidence of smoking, which was high in our population (41% current or ex-smokers). We would concur that an awareness of the limitations of non-invasive screening methods is required and that further emphasis should be placed on patient history as part of the screening process for SSc-related PAH.
The authors have declared no conflicts of interest.
References