title: Syndrome of inappropriate secretion of thyrotropin associated with thymoma-related peripheral nerve hyperexcitability.
abstract: Syndrome of inappropriate secretion of thyrotropin (SITSH) is a clinical state of inappropriately elevated secretion of thyrotropin (TSH) in the presence of elevated free thyroid hormones. Peripheral nerve hyperexcitability (PNH) is a rare disorder characterized by muscle twitching at rest. No relation between them is known. A 49-year-old man was referred to our hospital because of elevated serum free thyroxine (2.6 ng/dL; normal range, 0.9-1.7) and normal TSH (2.7 mIU/L; normal range, 0.5-5.0). Genetic analysis revealed no mutations of the thyroid hormone receptor β gene. Magnetic resonance imaging visualized no pituitary adenoma. He complained of appetite loss, weight loss, myokymia, paraesthesia, hyperhydrosis and insomnia. Chest X ray and computed tomography (CT) scan showed a mediastinal tumor diagnosed as a thymoma by CT-guided biopsy. Electromyography disclosed fasciculations and myokymic discharges. Nerve conduction studies showed prolonged after-discharges following evoked compound muscle action potential. The patient was diagnosed with thymoma-associated PNH based on neurological manifestations and neurophysiological findings, and was treated with pulse therapy with methylprednisolone after thymectomy. Interestingly, the SITSH state became less prominent as his neurological manifestations improved. This is the first case of SITSH possibly caused by thymoma-associated PNH.
authors.affiliation: Second Division, Department of Internal Medicine, Hamamatsu University School of Medicine, Hamamatsu 431-3192, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Ohba
authors.forename: Kentaro
authors.initials: K
authors.lastname: Shirakawa
authors.forename: Yuta
authors.initials: Y
authors.lastname: Okawa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Iwaki
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Matsunaga
authors.forename: Shingo
authors.initials: S
authors.lastname: Suzuki
authors.forename: Akio
authors.initials: A
authors.lastname: Matsushita
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Morita
authors.forename: Shigekazu
authors.initials: S
authors.lastname: Sasaki
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Oki
authors.forename: Hirotoshi
authors.initials: H
authors.lastname: Nakamura
mesh_terms: D006801:Humans; D008297:Male; D008775:Methylprednisolone / Q000627:therapeutic use; D008875:Middle Aged; D018696:Neuroprotective Agents / Q000627:therapeutic use; D010523:Peripheral Nervous System Diseases / Q000503:physiopathology* / Q000628:therapy; D013934:Thymectomy; D013945:Thymoma / Q000378:metabolism* / Q000628:therapy; D013953:Thymus Neoplasms / Q000378:metabolism* / Q000628:therapy; D013972:Thyrotropin / Q000378:metabolism*
chemical_list: D018696:Neuroprotective Agents; D013972:Thyrotropin; D008775:Methylprednisolone