Evaluation of the Biochemical Subtypes of Amyloidosis without Immunohistochemistry according to the Recommendations of the International Amyloidosis Nomenclature Committee: A Multicenter Study in Dakar Involving 41 Cases

Abstract

Introduction: Amyloidoses are a heterogeneous group of diseases characterized by extracellular deposits of insoluble fibrillar proteins in tissues. In sub-Saharan Africa, the epidemiology remains poorly understood, and the diagnosis of biochemical subtypes remains challenging in our clinical setting. The objective of our study was to determine the biochemical subtypes based on observed phenotypes, in accordance with international recommendations. Methods: This is a multicenter study combining a retrospective clinical review of hospital archives and an aggregation of cases documented in the scientific literature. All cases of histologically confirmed amyloidosis in patients over 16 years of age from January 1990 to October 2024 within level-3 national centers in Dakar were screened. Subtypes were systematically stratified into Confirmed (via immunohistochemistry/immunofluorescence), Probable (via predictive clinical phénotype and etiology guidelines), or Indeterminate categories. Results: A total of 41 cases were identified, including 18 men and 23 women (male-to-female ratio 0.78). The mean age was 59.93 ± 14.89 years. Regarding data sources, 36 cases (87.80%) were compiled from direct hospital archives and 5 cases (12.20%) were integrated from peer-reviewed publications. The most common manifestations were renal (75.61%, n = 31), cardiac (48.78%, n = 20), and gastrointestinal (39.02%, n = 16). The histological diagnosis was established via renal biopsy in 22 patients (53.65%), salivary gland biopsy in 13 patients (31.70%), skin biopsy in two patients (4.87%), bronchial biopsy in one patient (2.44%), and combined salivary-subcutaneous adipose tissue biopsy in three patients (7.31%). Definitive subtyping was Confirmed in only 3 cases (2 cases of AL and 1 case of AA). Based on phenotypes according to international guidelines, the remaining cases were classified as Probable AA in 20 patients, Probable AL in 12 patients, Probable senile ATTR in 2 patients, Probable beta-2-microglobulin in 2 patients, and Indeterminate in 2 patients. Sensitivity analysis excluding literature cases demonstrated no significant shift in subtype distribution. Chronic infectious or inflammatory etiologies underlaid all 21 AA cases, with tuberculosis alone accounting for 17.07% (n = 7) of the entire cohort. All AL amyloidosis cases were secondary to multiple myeloma. The 36-month survival rate was 60%, with age being the only factor statistically associated with death (p = 0.023). Conclusion: The incidence of amyloidosis in our region has been steadily increasing over the past decade. However, immunophenotyping remains highly inaccessible. Renal manifestations are the most common.