Case numbers and incidence of hospitalized amyloidosis patients are shown in Table
. For years 2001 to 2008, a total of 949 patients were identified, giving an incidence of 8.29 per million person-years. Unspecified amyloidosis was the largest disease category with 535 patients (incidence 4.69/million), follow by secondary systemic amyloidosis (136 patients, 1.18/million). Overall, men had a somewhat higher incidence than women (1.3-fold for unspecified amyloidosis), with the exception of secondary systemic amyloidosis for which the female incidence was 1.9 times the male rate.
Numbers and incidence rates (per million person- years) for hospitalized amyloidosis patients, 2001-2008
The age-specific rate of hospitalization for amyloidosis is shown in Figure
. Note that the scales of the y-axes vary. Secondary systemic amyloidosis showed a sharp male peak at age 70–74 years and a broader female peak with younger cases (A). Organ-limited amyloidosis reached a broad male maximum at age 65–79 years and the female maximum somewhat earlier; both male and female curves showed evidence on two main components (B). ‘Other’ amyloidosis types followed the same pattern (C) but for unspecified amyloidosis the male maximum at 65–69 years occurred earlier than the female maximum at 70–74 years (D).
Regional differences in the incidence of amyloidosis were analyzed by residence as of year 1990 (data not shown). The only significant differences (i.e., 95%CI did not overlap with ‘All’, IR 3.84, 95%CI 3.55-4.14) were found for unspecified amyloidosis for the provinces of Uppsala (n= 36, IR 6.93, 95%CI 4.67-9.20) and the neighboring province to the west, Västmanland (n= 38, IR 6.67, 95%CI 4.55-8.78). Importantly, no excess cases were found in the two northernmost provinces which are the endemic area of FAP
Causes of death were recorded for 1143 amyloidosis patients hospitalized between years 1997 through 2008, the longest period when subtypes were recorded (Table
). A total of 234 (21%) underlying causes of death were due to amyloidosis and 328 (29%) were due to other causes. Additionally, amyloidosis was given as a contributing cause of death for 17 patients. Among other underlying causes, deaths due to cancer were the most common cause and accounted for 16/40 cases in ‘other’ amyloidosis and 68/182 for unspecified amyloidosis. Diseases of the circulatory system predominated for secondary systemic and organ-limited amyloidosis. Myeloma would be pathognomonic of AL amyloidosis and it accounted for 5 (secondary systemic amyloidosis), 0 (organ-limited amyloidosis), 12 (other amyloidosis) and 24 (unspecified amyloidosis) deaths among these four subtypes, respectively. Incident myelomas were recorded for 7, 3, 13 and 21 patients, respectively. Thus, assuming that 10% of AL amyloidosis patients have myeloma at diagnosis
], the extrapolated AL amyloidosis case numbers were 70 (37% of secondary systemic amyloidosis), 30 (22% of organ-limited amyloidosis), 130 (80% of other amyloidosis) and 210 (32% of unspecified amyloidosis), adding up to 440 cases, which was 38% of all 1143 patients. Rheumatoid arthritis would be indicative of secondary systemic amyloidosis; 14/85 (17%) deaths in secondary systemic amyloidosis were due to rheumatoid arthritis, which was far above unspecified amyloidosis with 10/182 (5%) rheumatoid arthritis deaths.
Causes of death in hospitalized amyloidosis patients 1997-2008
For the estimation of the overall hospitalization rate for amyloidosis, we compared previous hospitalizations of the 197 patients whose underlying cause of death was amyloidosis in years 2005 through 2008. Of these, 151 were hospitalized any time from 1964 onwards for amyloidosis as the main or secondary diagnosis. Thus the hospitalization rate was at least 77% for this group of patients. However, the true rate is likely to be higher because the Hospital Discharge Registry reached nation-wide coverage not earlier than 1987 and the Outpatient Register was started in 2001
To assess the frequency of amyloidosis hospitalizations, amyloidosis patients were identified from years 1997 through 2000 and they were scored for the number of hospitalizations. Among 51 patients diagnosed with secondary systemic amyloidosis, 33 (65%) were hospitalized once, 9 twice and 9 three or more times. Among 27 patients diagnosed with organ-limited amyloidosis, 14 (52%) were hospitalized once, 2 twice and 11 three or more times. Among 39 patients diagnosed with other amyloidosis, 19 (49%) were hospitalized once, 4 twice and 16 three or more times. Among 125 patients diagnosed with unspecified amyloidosis, 50 (40%) were hospitalized once, 28 twice and 47 three or more times. This population of 242 patients, first diagnosed between years 1997 and 2000, was also analyzed in terms of change of amyloidosis diagnostic subtype between the first and the last discharge diagnoses. A change was noted for 23 patients (9.5%); 15 of these were initially diagnosed with unspecified amyloidosis, which was changed to ‘other’ amyloidosis among 7 patients and to hereditary amyloidosis among 4 patients (1.6% of 242 patients).
Kaplan-Meier survival curves were plotted for patients first diagnosed between years 1997 to 2000 according to their last discharge diagnosis from 1997 to 2008 (Figure
shows the curves for secondary systemic amyloidosis (median survival time 4 years) and unspecified amyloidosis (median survival time 3 years). Figure
shows the curves for organ-limited amyloidosis (median survival time 6 years) and ‘other’ amyloidosis (median survival time 3 years).
Figure 2 Kaplan-Meier survival estimates for the subtypes of hospitalized patients with amyloidosis by subtypes. The figures next to the graphs show the patients at risk in each year of follow-up. Figure
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