Thyrotoxicosis Presenting as Unilateral Drop Foot

Ultrasound measurement of vastus lateralis and vastus medialis muscle parameters to identify chronic thyrotoxic myopathy

Introduction

Chronic thyrotoxic myopathy (CTM) is a common, easily neglected complication of hyperthyroidism. There are currently no standard diagnostic criteria for CTM, and the ultrasonic characteristics of CTM-affected skeletal muscle remain unclear. Herein, we aimed to evaluate hyperthyroid patients for CTM by ultrasound and identify ultrasonic muscle parameter cutoffs for CTM diagnosis.

Materials and methods

Each participant underwent ultrasonography. The original (muscle thickness (MT), pennation angle (PA), and cross-sectional area (CSA)) and corrected (MT/height (HT), MT/body mass index (BMI), CSA/HT, and CSA/BMI) parameters of the vastus lateralis and vastus medialis (VM) were evaluated. The diagnostic effectiveness of ultrasound for predicting CTM was determined using receiver operating characteristic (ROC) curve analysis. Our study included 203 participants: 67 CTM patients (18 males, 49 females), 67 non-CTM patients (28 males, 39 females) and 69 healthy controls (20 males, 49 females).

Results

The CTM group had lower muscular ultrasonic and anthropometric parameters, higher thyroid hormone and thyroid-stimulating hormone receptor antibody (TRAb) levels, and a longer duration of hyperthyroidism than the non-CTM group (P < 0.05). The VM-PA, VM-CSA, VM-CSA/HT, and VM-CSA/BMI were lower in females than in males (P < 0.05). Free thyroxine (FT4) and TRAb both showed significant negative correlations with VM-MT, VM-MT/HT, VM-CSA, and VM-CSA/HT (P < 0.05). VM-MT/BMI and VM-CSA/HT, respectively, best predicted male and female CTM (AUC = 0.84, 0.85; cutoff ≤ 0.07, < 4.01).

Conclusion

Ultrasound measurement of muscular parameters, especially in the VM, is a valid and feasible way of diagnosing and characterizing possible CTM in hyperthyroidism.

Recurrent thyrotoxic periodic paralysis with normokalemia in a 36-year-old man: A case report

Among patients with thyrotoxicosis and proximal muscle weakness, some patients with TPP may present with apparent normokalemia in whom a careful administration of potassium may lead to rapid reversal of muscle weakness.

[A case of thyrotoxic myopathy with generalized body muscular atrophy including the tongue muscle, lacking physical manifestations of Basedow disease]

We report a 74-year-old man with a 2-year history of proximal limb pain, body weight loss of 15 kg, and muscle weakness. Muscle atrophy was evident in the limbs and trunk, as well as the tongue. He was admitted to our hospital with suspected amyotrophic lateral sclerosis (ALS). Although he had no physical manifestations of Basedow disease such as palpitations, hyperhidrosis, hand tremor, exophthalmos, and an enlarged thyroid, he was diagnosed as having thyrotoxic myopathy as laboratory examinations indicated hyperthyroidism and positivity for TSH receptor antibody. The serum level of soluble IL-2 receptor was also elevated. Despite the severe muscle atrophy, the serum CK level was normal. A biopsy from the left quadriceps muscle revealed Type 1 fibers atrophy. Administration of anti-thyroid drugs normalized his thyroid function and the level of soluble IL-2 receptor, leading to improvement of the generalized muscle atrophy.