An unusual clinical presentation of a rare tumor of the thyroid gland: report on one case of leiomyosarcoma and review of literature.

Primary muscle tumors of the thyroid gland are exceedingly rare. We report on the case of a patient with primary leiomyosarcoma of the thyroid gland and review the literature. An 83-year-old woman complaining of neuropathic pain in her left arm and enlargement of her anterior neck underwent multiple surgical biopsies of the thyroid gland. The tumor was composed of interlacing fascicles of spindle-shaped cells that expressed smooth muscle actin and vimentin but were negative for cytokeratins and thyroglobulin. Ultrastructurally, bundles of myofilaments were present. Magnetic resonance imaging showed a thyroid tumor that directly extended to the adjacent vertebra with an associated pachymeningitis. The patient died 2 months after surgery. The diagnosis of primary leiomyosarcoma of the thyroid gland is difficult and requires numerous clinical, radiologic, and pathologic data. To our knowledge, this case is the first one with such a locoregional extension.