Microfasciculation: a morphological pattern in leprosy nerve damage

Antunes S L G, Medeiros M F, Corte‐Real S, Jardim M R, da Costa Nery J A, Hacker M A V B, da Costa Valentim V, Amadeu T P & Sarno E N (2011) Histopathology58, 304–311 Microfasciculation: a morphological pattern in leprosy nerve damage Aims: To study Microfasciculation, a perineurial response found in neuropathies, emphasizing its frequency, detailed morphological characteristics and biological significance in pure neural leprosy (PNL), post‐treatment leprosy neuropathy (PTLN) and non‐leprosy neuropathies (NLN). Methods and results: Morphological characteristics of microfascicles were examined via histological staining methods, immunohistochemical expression of neural markers and transmission electronmicroscopy. The detection of microfasciculation in 18 nerve biopsy specimens [12 PNL, six PTLN but not in the NLN group, was associated strongly with perineurial damage and the presence of a multibacillary inflammatory process in the nerves, particularly in the perineurium. Immunoreactivity to anti‐S100 protein, anti‐neurofilament, anti‐nerve growth receptor and anti‐myelin basic protein immunoreactivity was found within microfascicles. Ultrastructural examination of three biopsies showed that fibroblast–perineurial cells were devoid of basement membrane despite perineurial‐like NGFr immunoreactivity. Morphological evidence demonstrated that multipotent pericytes from inflammation‐activated microvessels could be the origin of fibroblast–perineurial cells. Conclusions: A microfasciculation pattern was found in 10% of leprosy‐affected nerves. The microfascicles were composed predominantly of unmyelinated fibres and denervated Schwann cells (SCs) surrounded by fibroblast–perineurial cells. This pattern was found more frequently in leprosy nerves with acid‐fast bacilli (AFB) and perineurial damage while undergoing an inflammatory process. Further experimental studies are necessary to elucidate microfascicle formation.