Abnormal substances can deposit in the myocardium either in the extracellular space (infiltration) or in cells (storage). Infiltration may be cells (inflammatory, histiocytosis, or tumour) or amyloid fibrils [in ventricular myocardium light chain-related (AL) or transthyretin-related (TTR), wild-type or mutant]. Storage may be glycogen (glycogen storage diseases, Danon), lipid (Fabry, Gaucher), mucopolysaccharidoses, or iron. Iron, malignancy, and inflammation (myocarditis) are covered elsewhere. Amyloid and storage diseases are typically systemic multi-organ disease, with ‘red flag’ clinical features often present. They mainly cause heart muscle disease, with hypertrophy mimicking hypertrophic cardiomyopathy. All are relatively rare and often diagnosed late when therapies are less effective. Imaging structural and functional changes provide pointers to the underlying aetiology and additional features may be present (perfusion defects, valve disease, atrial thickening), but it is in myocardial tissue characterization where CMR adds real value. In amyloid, deposition appears to proceed stepwise, with initial subendocardial, and later transmural, late gadolinium enhancement (LGE). Myocardial nulling may be difficult, requiring the phase-sensitive inversion recovery (PSIR) technique. In Fabry disease, a characteristic initial basal inferolateral LGE pattern occurs, later with extensive LGE, leading to dilatation and impairment. Mapping adds value. In amyloid, both native T1 and the ECV are very high. Both are prognostic and candidates for surrogate endpoints in drug development studies. In Fabry disease, native T1 is low, reflecting lipid storage, and may occur early before hypertrophy. The LGE area usually has T2 elevation correlating with blood troponin, which suggests inflammation as part of disease development.
