The incidence of diphtheria in the developed countries has steadily declined following effective immunization program since the 1920’s. However, resurgence had been observed mainly due to waning immunity in adults. In developing countries, the disease is still endemic and responsible for high case fatality [1] [2] .

Corynebacterium diphtheria produces exotoxins which cause DNA fragmentation and cytolysis by inhibiting elongation factor-2 activity in protein synthesis in addition to damage to conduction tissue [3] [4] . The myocardium also shows hyaline degeneration and necrosis. This results in development of myocarditis in patients with diphtheria. Myocarditis may occur in about 10% - 25% of patients with respiratory diphtheria and it is considered the most serious complication with high reported mortality [5] [6] . The risk of developing cardiac toxicity is proportional to the severity of local infection. Diphtheria myocarditis is frequently manifested by arrhythmias that can cause sudden death if not managed properly. The patients with cardiac involvement may be asymptomatic (changes in electrocardiogram (ECG) and/or raised cardiac enzymes) or symptomatic (features of heart failure) [7] .

In India, diphtheria still remains endemic and associated with fulminant complications and mortality [8] . Several factors like inadequate vaccine coverage, poor socio-economic status, delayed reporting, and delayed administration or unavailability of diphtheria antitoxin further contribute to high mortality [9] . Even though, there was higher prevalence of the disease in India, we found the scarcity of literature which focused on the incidence, clinical profile as well as clinical outcomes of myocarditis in the patients diagnosed with diphtheria myocarditis. So, we design the study to address clinical profile, clinical outcomes as well as immunization status of the patients diagnosed with diphtheria myocarditis in Indian scenario.

Thirty-three patients with diphtheritic myocarditis were studied during the study period. The demographic and clinical characteristics of the patients are outlined in Table 1. Out of 33 patients 18 were males, 15 were females. The age group, most commonly affected, was 5 - 10 years (15 patients) which was followed by age group 10 - 15 years (8 patients). The common clinical features were fever (n = 32), throat pain (n = 31) and difficulty in swallowing (n = 30).

In India, the incidence of diphtheria myocarditis varies from 16% to 66% [10] [11] . Havaldar et al. had carried out the study for the period of 10 years and he found that myocarditis was becoming major cause of death (8 out of 16 deaths) in patients with diphtheria by gradually replacing major cause of death i.e. laryngeal obstruction or post-tracheostomy complications [12] . Myocarditis is reported to be the only independent predictor of death in patients with diphtheria [11] . The study conducted in India between January 1998 to December 2012 also demonstrated myocarditis was responsible to 66.6% deaths in patients with diphtheria [8] . So to determine the clinical profile and clinical outcomes of patients with diphtheritic myocarditis, we carried out this study.

In our study, the majority of the cases were noted in the age group of 5 - 10 years (45.5% patients) and there was no sex difference in the occurrence of the disease.

It has been proved that diphtheria vaccine is one of the major approaches for the control and prevention of diphtheria (at least 90% coverage). The recommended schedule for immunization (for diphtheria) in India is as follow: For infants—a series of four doses given at two, four, six, and 15 - 18 months of age. A fifth shot, or booster dose, is recommended at 4 - 6 years of age, unless the fourth dose was given late (after the fourth birthday). Because immunity to diphtheria wanes with time, individuals should receive a booster dose of tetanus- diphtheria toxoid every ten years.

In India, major reason for higher incidence of diphtheria in children may be inadequate immunization. It has been observed in our study also that out of 33 patients of the study, only 1 patient was adequately immunized whereas 30 patients were unimmunized. Majority of the unimmunized patients belonged to the age group of 5 - 10 years.

The clinical signs of cardiac involvement in diphtheria are non-specific. There were 28 patients who experienced conduction abnormality and it is noteworthy that out of these 28 patients, 24 patients died. All the patients who developed LBBB died during hospitalization. The study carried out by M. M et al. also showed that the patients with diphtheria who developed myocarditis presented with conduction blocks and arrhythmias [8] .

Celik et al. also demonstrated that the patients with LBBB and T wave inversion at hospital discharge had lower survival rates than that of the patients without these ECG changes in their long term follow-up [13] . They even identified LBBB and T wave inversion as the independent predictors of survival in diphtheritic myocarditis. In our study, the mortality rate of diphtheria myocarditis was 72.7% which is higher than that of the study carried out by Stockins et al. in which mortality rate was 46% [14] .

The incidence of diphtheria has increased in recent years and the most common age group affected is 5 - 10 years, with no sex difference in occurrence. Most of the patients with diphtheria presented with asymptomatic myocarditis and those who presented with either LBBB alone or with combination of other conduction abnormalities depicted high mortality rate.