IPH is a rare cause of
DAH resulting in deposition and accumulation of haemosiderin in the lungs [1,2]. Knowledge of this entity is limited, and the
diagnosis is often delayed by 2-3 years [1-4]. The diagnostic challenge of this
condition poses a significant issue as some patients may present in acute
respiratory failure, and disease progression can result in pulmonary fibrosis
and end-stage lung disease [1]. This condition is more commonly reported in the
paediatric population which accounts for more than 80% of reported cases [1-5].
The estimated incidence ranges from 0.24 to 1.23 cases per million [6,7],
whilst the prevalence in a single hospital retrospective study in the United
States is estimated to be 6.71 cases per million patients in the paediatric
cohort [8]. The incidence and prevalence of this condition is largely unknown
in the adult population. In a recent retrospective review of literature, there
has been a total of 84 reported adult cases from 1950 to 2021 [3]. Of these
patients, the majority were males (64.3%), and the median age was 27 years [3,9].
In adults, the course is often prolonged, symptoms less pronounced, and the
prognosis may be more favourable compared to children, although data remains
limited [1,3,5,12].
The pathogenesis of IPH
still largely remains unknown, although an autoimmune mechanism has gained
momentum from the identification of autoantibodies and response to
corticosteroid therapy [1,2,4,5]. Saha et al. reported approximately one in
five patients in an adult cohort population testing positive for an
autoantibody, with antibodies specific for coeliac disease (CD) being the most
common [3]. The co-existence of IPH and CD has been described as Lane-Hamilton
syndrome (LHS) [1-,4,11]. Interestingly, most patients with LHS do not suffer
from gastrointestinal symptoms, and many studies have recommended testing for
coeliac antibodies when diagnosed with IPH [3,11]. A gluten-free diet has been
associated with improved respiratory symptoms and long-term outcomes in these
patients [2,11]. Other commonly reported autoantibodies in adults include
rheumatoid factor and anti-thyroid antibodies. Previous studies have also
suggested a complex interplay involving genetic, allergic, and environmental
factors. No specific genetic markers have been identified yet, however the
possibility of a genetic predisposition is suggested by several reports
describing familial clustering of cases [9]. A retrospective database review
has shown that Down Syndrome has been associated with pulmonary hypertension
and worse prognosis [2,5,10]. The allergic hypothesis stems from the isolation
of plasma antibodies against cow’s milk protein (IgE and IgG) in children
diagnosed with IPH [1,2,5] however no prospective studies have validated this
association and testing against cow’s milk protein is controversial.
Environmental exposure to second-hand smoking, highly potent fungal toxin
(particularly Stachybotrys chartarum), and pesticides have been associated
with pulmonary haemorrhage [1,2,5]. The mechanism for lung injury involves
excessive iron deposition, possibly inefficient handling of the iron load by the
alveolar macrophages, oxidative damage, inflammation, and eventual fibrosis [1,2,9].
The clinical presentation
of IPH in the adult population is highly variable [1,4]. Patients often present
with intermittent episodes of haemoptysis interspersed between periods of
relative normalcy [1,2]. Haemoptysis ranges from intermittent, scanty, to daily
frank bleeding and occasionally, massive haemorrhage resulting in acute
respiratory failure [1,2]. Most patients develop iron deficiency anaemia from
blood loss in the lung. In the recent largest retrospective review to date,
there appeared to be a higher reported incidence of symptoms compared to
previous reviews. Signs and symptoms include anaemia (91.6%), dyspnoea (85.5%),
haemoptysis (26.2%), and chest pain (10.7%) [3]. The classical triad comprising
of haemoptysis, anaemia, and radiologic chest abnormalities was present in
almost 80% of patients [3-5]. Systemic symptoms, such as fever, night sweats,
weight loss, or loss of appetite was seen in nearly half of the patients (45%).
This is a significant finding given that the presence of fever and other
non-specific systemic symptoms may incorrectly dissuade clinicians from
considering the diagnosis IPH and lean towards an infectious aetiology for the
respiratory symptoms, resulting in a delay in diagnosis [3].