Thyrotoxic myopathy mimicking myasthenic syndrome associated with thymic hyperplasia

Intern Med. 2008;47(5):445-7. doi: 10.2169/internalmedicine.47.0682. Epub 2008 Mar 3.

Abstract

A 41-year-old man with progressive limb weakness manifested fluctuating muscle weakness as seen in myasthenia gravis (MG). Laboratory investigations revealed hyperthyroidism without the complication of MG. Electrophysiological studies demonstrated abnormal features of neuromuscular transmissions resembling those of the Lambert-Eaton myasthenic syndrome rather than those of MG. A CT scan showed a mediastinal mass that suggested thymic hyperplasia which often complicates MG or hyperthyroidism. Medical treatment of hyperthyroidism resulted in resolution of MG-like symptoms and regression of thymic hyperplasia on CT concomitant with normalization of thyroid function. This case highlights the fact that careful investigations are needed to differentiate MG-like symptoms from genuine MG in cases of hyperthyroidism with thymic lesions.

Publication types

  • Case Reports

MeSH terms

  • Adult
  • Antithyroid Agents / therapeutic use
  • Diagnosis, Differential
  • Graves Disease / complications*
  • Graves Disease / diagnosis
  • Humans
  • Male
  • Methimazole / therapeutic use
  • Muscle Weakness / etiology*
  • Myasthenia Gravis / diagnosis
  • Thymus Hyperplasia / complications
  • Thymus Hyperplasia / diagnosis
  • Thymus Hyperplasia / drug therapy
  • Thymus Hyperplasia / physiopathology*
  • Thyrotoxicosis / complications*

Substances

  • Antithyroid Agents
  • Methimazole