Discussion

Apical hypertrophic cardiomyopathy is a phenotypic variant of hypertrophic cardiomyopathy, characterised by left ventricular hypertrophy limited to the distal apex. Initially described in Japan, where it accounts for approximately 25% of all cases of hypertrophic cardiomyopathy, it is a relatively rare finding outside this population, with a reported prevalence of 1–3%. ^{Reference Kitaoka, Doi, Casey, Hitomi, Furuno and Maron2} To date, only very few cases of apical hypetrophic cardiomyopathy in subjects younger than 18 years have been described, ^{Reference Miyamoto, Horigome, Kawano and Sumazaki3–Reference Maurizi, Passantino and Spaziani6} of whom only one was reported to be symptomatic, presenting with exertional chest pain. ^{Reference Zhao, He and Liu4} Due to its rare presentation in childhood and adolescence and to intrinsic limitations of echocardiography in displaying left ventricular apex, particularly in instances of poor echogenic windows, high grade of awareness is required when approaching this cohort of patients. The diagnosis of apical hypertrophic cardiomyopathy may frequently be missed despite consistent symptoms and electrocardiogram changes if the initial echocardiographic evaluation does not provide evidence of cardiomyopathy. In the presence of otherwise unexplained symptoms and/or electrocardiogram findings and persistent clinical suspicion of structural heart disease, it is therefore essential to refer such patients to a second line imaging assessment. As it overcomes the technical limitations imposed to echocardiography, cardiovascular magnetic resonance imaging has established itself as the gold standard for the diagnosis and previous studies have shown that echocardiography can miss the diagnosis in 40% of later by cardiovascular magnetic resonance imaging-detected apical hypertrophic cardiomyopathies. ^{Reference Hughes, Knott and Malcomoson1} In our case, identifying apical hypertrophy was only possible referring the patient to cardiovascular magnetic resonance imaging, which was partly due to the pectus excavatum. Besides to accurate estimation, of biventricular morphology and function, cardiovascular magnetic resonance imaging allows the assessment of tissue fibrosis by evaluating late gadolinium enhancement. In our report, subendocardial distribution of gadolinium was observed in the left ventricular apical region. In apical hypertrophic cardiomyopathy, apical and subendocardial late gadolinium enhancement patterns are typically reported, ^{Reference Kim, Kim and Hwang7} supporting the hypothesis that apical ischaemia due to a mismatch between blood supply and increased oxygen demand in the hypertrophied myocardium might play a pathogenic role in the formation of fibrotic tissue. After careful review of literature, we found only one patient under 18 years, in whom cardiovascular magnetic resonance imaging – late gadolinium enhancement sequences were performed, documenting the apical distribution of the contrast agent. Although data regarding the paediatric population are lacking, hypertrophic cardiomyopathy registry data including 2755 middle-aged patients documented late gadolinium enhancement in 45.8% of subjects presenting the apical variant of the disease. ^{Reference Neubauer, Kolm and Ho8} Apical hypertrophic cardiomyopathy patients demonstrating late gadolinium enhancement on the magnetic resonance imaging were reported to experience more severe symptoms and more episodes of non-sustained ventricular tachycardia on Holter electrocardiogram monitoring compared to those without late gadolinium enhancement, suggesting that areas of fibrosis might represent potential arrhythmogenic substrates. ^{Reference Kebed, Al Adham and Bishu9,Reference Amano, Tacheda and Tachy10}

As it typically presents with apical obliteration and subendocardial distribution of late gadolinium enhancement, endomyocardial fibrosis may potentially mimic apical hypertrophic cardiomyopathy, making it challenging, to differentiate between these two pathological entities. Although being endemic in Africa, endomyocardial fibrosis was also described in Europe and affects predominantly children and young adults with a bimodal distribution peaking at 10 and 30 years of age. Clinical presentation and presence of eosinophilia are variable and to date no specific laboratory test for the diagnosis of endomyocardial fibrosis is available. As it provides optimal visualisation of the ventricular apex, cardiovascular magnetic resonance imaging is a fruitful tool. In our patient, obliteration was only observed in systole, whereas in endomyocardial fibrosis, being related to the presence of mural thrombus, it is constant during the entire cardiac cycle. The triple-layered pattern of late gadolinium enhancement typically described in endomyocardial fibrosis (V sign) was not documented in our case. Taking in account also the absence of other imaging features consistent with endomyocardial fibrosis (atrioventricular valve dysfunction, restrictive pattern across atrioventricular valves) and the negative history for fever and travelling to tropical regions abroad, we excluded this diagnosis. ^{Reference Dato11}