Systemic lupus erythematosus (SLE) is an auto-immune disease frequently associated with pulmonary and cardiovascular complications in humans, even in the absence of associated or concomitant connective tissue disease. Nevertheless, the effects of SLE on the pulmonary vasculatures have not been extensively studied or reviewed. Pulmonary hypertension (PH) is one of severe manifestations of (SLE). Due to improvement in the current understanding of the pathogenesis and pathology of these diseases, improved methodology in the conduct of advanced research and advancement of successful medical, and surgical therapies; our understanding of SLE associated PH has evolved dramatically. In this paper we will review the previous and current evidence regarding the prevalence, clinical parameters, prognostic implications and survival rates in SLE associated PH. Accordingly, we will review and contrast the association between these two conditions, highlighting the clinical features, discussing the methodological limitations of existing data on prevalence, treatment options and survival; and draw special attention to special situations, in particular pregnancy.
Systemic lupus erythematosus (SLE) is an autoimmune diseases and is associated with pulmonary and cardiovascular complications. Even though pulmonary hypertension (PH) has less often been reported as one of the manifestations in SLE patients, both invasive and non-invasive exercise hemodynamics have been previously reported to be abnormal in these patients [1, 2]. Majority of patients with SLE present with marked decrease in exercise capacity compared with normal individuals [1, 2]. The exercise intolerance in these patients could be multifactorial as they do present with easy fatigability, physical deconditioning, musculoskeletal and neurological abnormalities, which poses challenges when managing patients with SLE [3, 4].
In addition to cardiopulmonary complications of SLE, the five criteria of pulmonary hypertension based on the current World Health Organization classification have been reported [5, 6]. Pulmonary hypertension in SLE patients may also occur as a result of concomitant pulmonary diseases, and it could also result from associated pulmonary vasculitis and chronic thrombotic diseases.
Although the prevalence of PH in SLE patients could be variable, previous studies reported the prevalence of PH in these patients to be ranging between 0.5% and 45%, however these are old studies [7 -12, 13- 16]. However some recent studies have estimated the prevalence of SLE associated PH to be below 20% [17-19] . The pivotal factor leading to this wide variation is the diagnostic method used to evaluate the magnitude of pulmonary arterial systolic pressure in these patients. In addition, the variation could be related to inadequate information provided in regards to the underlying etiology of the PH. Despite these pitfalls, the association between SLE and PH or SLE associated PH seems to be increasing over time. Serial echocardiographic studies have demonstrated an increase in prevalence of PH; with reported prevalence rising from 14% to 43% over 3-5 years of follow-up period [1, 11] .
Clinical demographics and risk factors
Clinical manifestations of SLE associated PH vary, however the commonly reported features in these patients include insidious onset of dyspnea, easy fatigability, cough and chest discomfort. Unfortunately, these symptoms may develop late in the course of the disease. The pathological pulmonary vascular changes may be far more advanced by the time these patients present for their initial consultation with their primary physician, as a result SLE associated PH should be excluded in SLE patients presenting with these symptoms.
The characteristics of patients with SLE associated PH are similar to those of patients with idiopathic pulmonary arterial hypertension (IPAH), as a result it might be challenging to separate the two pathological entities during clinical evaluation. Even though there is no clear association between the duration of SLE and the development of PH, patients with SLE seem to develop PH within the first five years of the disease entity. Most interestingly PH may be the only sole clinical manifestation in some patients with SLE  . Some reports mentioned that there is no association between the presence of PH and degree, severity or activity of SLE based on the serology or activity markers; however this is very controversial as some reports have reported some association [7, 12, 21] .
The treatment modalities for SLE associated PH are similar to those of IAPH which include: oxygen, anticoagulation, vasodilators and calcium channel blockers. Different therapeutic modalities have previously been tried in these patients with no individual therapeutic regimen shown to be superior to others in managing SLE associated PH [22-28] . Different vasodilators have been previously tried and proved to be effective in most patients, and these include both selective and nonselective endothelin receptor inhibitors, phosphodiesterase-5-inhibitors, and different prostanoids regimens [1, 22-28, 29-31] .
Most patients with SLE associated PH receiving vasodilators demonstrated significant improvement in terms of New York Heart association Functional Class, exercise capacity, quality of life and delayed diseases progression [29-31] .
Clinical and sustained hemodynamic improvement has been reported after intensive immunosuppressive therapy which includes a combination of intravenous cyclophosphamide and high tapering doses of oral glucocorticoids [32-34] .
The surgical options for the management of SLE associated PH are similar to those used for other types of PH in patients who have failed optimal medical therapy. Atrial septostomy, lung or a combination of heart-lung transplantation are options in some patients with SLE associated PH. The main limitation for considering the surgical intervention in SLE associated PH is multiorgan involvement from the systemic disease and complications from the underlying co-morbidities which deem most patients unsuitable for surgical intervention. Although IAPH has been reported to have a better prognosis compared with SLE associated PH, some patients with SLE associated PH do much better if treated early [35-36] .
One- and three-year survival rates for SLE-associated PH have been reported to be 78% and 74% respectively [37-38, 21] . However a one-year survival rate has been reported above 90% and this improvement has been attributed to early introduction of advanced medical therapy which includes immunosuppression [39-40, 21] . Despite these advancements, if other respiratory disorders coexist with PH, the prognosis remains poor in these patients. Despite advancement in medical therapies the survival rate for IAPH remains better compared with SLE associated PH. The prognosis is much worse for those with concomitant respiratory disorders.
One special situation which needs special attention is pregnancy. Pregnancy should be discouraged in patients with SLE or SLE associated PH, as pregnancy can exacerbate underlying SLE and it is also recommended as an absolute contraindication in patients with PH [1, 41] . SLE associated PH has been reported to be common among women of child bearing age, and for that reason pregnant mothers should be screened for PH as the maternal mortality is quite high in this group [42-43] .The maternal mortality secondary to SLE associated PH has been reported to be extremely high, even higher than that related to any other pulmonary vascular disease in pregnancy [42-45] .
Although recent studies have reported better survival in SLE associated PH due to the introduction of advanced medical therapy, SLE associated PH is generally associated with high mortality rates [35-36] . Due tothese reported data on poor outcomes in this population, pregnancy should be discouraged in women of childbearing age with SLE or SLE associated PH; and therefore it should be mandatory to recommend screening for SLE or SLE associated PH in women of child bearing age.