A 35 year-old asymptomatic Caucasian female with a significant family history of hypertrophic cardiomyopathy (HCM), including sudden cardiac death of unknown cause in one son and HCM in two other children, was referred for cardiologic consultation. The electrocardiogram and transthoracic echocardiogram had revealed no abnormalities. Cardiovascular magnetic resonance (CMR) was performed for further assessment of myocardial function and detection of myocardial scar. Two-, three- and four-chamber CMR cines were obtained using steady-state free precession and inversion-recovery imaging was used to assess late gadolinium enhancement (LGE). CMR showed normal left ventricular (LV) systolic function (end-systolic volume index 24 mL/m²; end-diastolic volume index 72 mL/m², ejection fraction 63%) and normal wall thickness (anteroseptal wall thickness 0.8 cm, posterolateral wall thickness 0.8 cm). There was extensive, diffuse, poorly demarcated LGE throughout the LV ventricle, predominantly involving the basal lateral, basal anteroseptal and mid-inferior walls (figures 1A and 1B). Subsequent genotyping showed she was heterozygous for the mis-sense mutation 275G>A (R92Q) in exon 9 of the cardiac troponin T gene (TNNT2) previously reported to be associated with HCM [1, 2]. The same gene defect was also found in both surviving children with HCM.

Myocardial scar in HCM shows wide variation. Longitudinal stripes of fibrosis commonly occur at the junctions of the interventricular septum and free wall of the right ventricle (right ventricular insertion points), but more advanced forms include dense replacement scars throughout the ventricle [3]. Myocardial scar in HCM may serve as an arrhythmogenic substrate and the extent of area involved has been shown an association with arrhythmias, sudden cardiac death and major adverse cardiovascular events [3–5]. Diffuse LGE on CMR without left ventricular hypertrophy or enlargement is uncommon in HCM. LGE represents myocardial fibrosis in HCM, and therefore, with such diffuse pattern of myocardial scarring, left ventricular function might be expected to be depressed. The presence of diffuse LGE in a patient with an unequivocal HCM genotype and family history in the setting of an unequivocal normal cardiac phenotype has not been reported previously. This indicates that cardiac fibrosis may be the only demonstrable abnormality in HCM, and precede other phenotypic expression in HCM. This finding has important potential implications for family screening in HCM. Further evaluation of the need to include LGE CMR as routine practice to screen relatives of patients with HCM is required.