Histopathological Approach in Diagnosis of Mycetoma Causative Agents: A Mini Review

Abstract

Mycetoma is a unique neglected tropical disease which distributed worldwide and endemic in tropical and subtropical regions. This disease is caused by a large number of micro-organisms of fungal (eumycetoma) or bacterial (Actinomycitoma) origins. The disease is characterized by a swelling in the cutaneous and subcutaneous tissues, with the formation of sinuses tract in some patients with numerous deformities and disabilities. Mycetoma infection affects all ages. The diagnosis of the mycetoma is based on identification of the causative organism and the disease extension which in turn considered as the first steps in the management of the affected patients and eventually predicting disease treatment outcome and prognosis. Different diagnostic tools were developed that aimed to identify the causatives agent. These include direct microscopy, Fine needle aspiration, Imprint cytology, histopathological, culturing techniques and molecular identification. Since histopathology is continues to be a rapid diagnostic tool as well as cost effective means of providing a presumptive or/and in some instances a definitive diagnosis of an invasive mycetoma infection, as well as it able to detect the causative agents invasion of tissues and vessels as well as host tissue reaction to the causative agents, however no way to replace the culture and molecular diagnosis that remain the most powerful tools for the definitive diagnosis of the causative agents. In our clinical setting at Mycetoma Research center the histopathology report, considered as a powerful tool as it include a comment stating the morphological appearance of the causative agents and the type of the host tissue reactions as well as it stated clearly the possible differential diagnosis. In this review we will discuss varies histopathological appearance of mycetoma causative agents as well as the common used histochemical stains that can aid in the diagnosis and the host tissue reaction to varies causative agents.

Comparing the performance of the common used eumycetoma diagnostic tests

“…The specificity of culture (85.7%) was higher than histopathology (42.8%) because many of the grains may be difficult to identify in histopathological sections. In general, M. mycetomatis grains can be filamentous, vesicular or a combination of the two and can have amorphous cement material throughout the grain or only on the periphery 7,15,25 . In the histopathological reports, we noted that all black grains were identified as M. mycetomatis .…”

“…In general, M. mycetomatis grains can be filamentous, vesicular or a combination of the two and can have amorphous cement material throughout the grain or only on the periphery. 7,15,25 In the histopathological reports, we noted that all black grains were identified as M. mycetomatis. Furthermore, in Sudan, other black grain causative microorganisms are rare, and their histological appearance is not well known.…”

“…Formalin blocks were prepared, and from each block, a single section was cut using a rotary microtome (Leica, Germany) at 3–5 μm thickness. Sections were then stained with haematoxylin and eosin (H&E) and reported according to previously published criteria 7,15 …”

“…However, the diagnostic performance of these assays compared to the other common diagnostic assays has not been established in endemic regions. Given the misidentifications obtained by culturing, the currently available diagnostic tools should be validated using molecular identification by ITS sequencing as the gold standard, rather than culture 7 …”

“…[4][5][6] The most common causative agent of mycetoma is the fungus Madurella mycetomatis, accounting for more than 40% of the patients reported. 4,7 M. mycetomatis forms black grains in the infected tissue (Figure 1).…”