Diffuse intraneural leiomyoma in a case of sensorimotor neuropathy

Abstract

Leiomyomas are benign smooth muscle tumors, usually characterized by well-deWned Wbrous pseudocapsule and intersecting fascicles of spindle cells [3]. Few cases of leiomyomas in the peripheral nervous system (PNS) causing external nerve compression have been described [1, 7]. We report the case of a 71-year-old man who was referred for a 2 years history of burning pain and paresthesias associated with slowly progressive weakness of the lower limbs. He underwent total colectomy for diVuse polyposis 2 years before. Neurological examination and nerve conduction studies revealed symmetric sensorimotor axonal neuropathy of the lower limbs. Since all immunological, hematological and cerebrospinal Xuid examinations were negative, a sural nerve biopsy was performed. On semithin plastic sections, a mild degree of endoneurial Wbrosis, reduction of myelinated Wbers and signs of acute axonal degeneration were evident. Some fascicles had greater myelinated Wber loss than others, primarily in the center of the fascicles. Interestingly, paraYn-embedded, hematoxylin and eosinstained sections showed in epineurial and endoneurial perivascular spaces atypical large cells with abundant eosinophilic cytoplasm. Upon electron microscopy, these cells exhibited a basement membrane and prominent pinocytotic vesicles at the periphery (Fig. 1). The cytoplasm was Wlled with actin and myosin Wlaments, aggregates of glycogen particles and few organelles. Some cells showed oval and centrally located nuclei. Immunohistochemically, they were positive for smooth muscle actin, desmin and calponin (Fig. 2), but negative for CD31, cytokeratin and S-100 protein, demonstrating that they were smooth muscle cells (SMC). These cells did not show proliferative activity (negativity for Ki-67). Neither necrosis nor a deWnite capsule were present. The morphological and immunohistochemical data suggested a diagnosis of leiomyoma. This is the Wrst description of a diVuse SMC inWltrate of the PNS, both in the endoneurium and epineurium, whereas well circumscribed and encapsulated leiomyomas have occasionally been reported in the PNS. Other potential tumors such as leiomyosarcoma, schwannoma and hemangioma have to be considered in the diVerential diagnosis, but can be excluded based on immunoproWle [2]. Several hypotheses can be envisaged for the possible cellular origin of this unique tumor in the PNS, including pluripotential mesenchymal cells, perivascular connective tissue elements or SMC of blood vessels [6]. Epineurial proliferation of SMC in sural nerve biopsies indicating inXammatory or non-inXammatory angiopathy has been described before [5]. However, our patient’s sural nerve biopsy revealed SMC also in the endoneurium without signs of angiopathy, suggesting a diVerent origin of SMC. How this inWltrate caused damage of peripheral nerve Wbers remains unclear. Our patient’s clinical presentation suggests a diVuse damage of the PNS, while nerve biopsy Wndings associated with F. Cerri (&) Department of Neurology and INSPE, San RaVaele ScientiWc Institute, Via Olgettina, 6