Interstitial cell infiltrate and myocardial fibrosis in dilated cardiomyopathy: A special type of cardiomegaly corresponding to sequelae of myocarditis

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Abstract
We examined the relationship between interstitial cell infiltration and myocardial fibrosis in patients with clinically diagnosed dilated cardiomyopathy (DCM). Forty-two cases of DCM were divided into two groups, according to the mean number of the interstitial round cells per 10.2×104 square µm (Nic): the inflammatory group (Nic ≥5) and noninflammatory group (Nic<5). The 12 cases in the inflammatory group were clinically similar to the 30 cases in the non-inflammatory group, but the inflammatory group exhibited a significantly (P<0.001) larger area of myocardial fibrosis (34.8%±12.8% vs 17.5%±8.2%), a significantly (P<0.01) higher frequency of diffuse perimyocytic-type fibrosis (83% vs 23%), fewer myocardial cells in the left ventricular wall (170±70 fibers vs 216±81 fibers), and significantly (P<0.01) greater hypertrophy of the myocytes (18.3±3.4 vs 15.3±2.7 µm). In addition, cases exhibiting marked fibrosis (fibrosis area ≥25% of the myocardium) had a significantly higher Nic score (8.3±6.8) compared to cases with the less fibrotic type of DCM (4.0±5.7). We speculate that persistent or preceding inflammatory cell infiltration induces the myocardial fibrosis, especially the diffuse perimyocytic type, in the fibrosis-predominant type of DCM. Therefore, most of these cases may be a sequela of myocarditis, and more correctly termed post-myocarditic cardiomegaly.