Cervical spine MRI findings leading to diagnosis of hypothyroid myopathy in dropped head syndrome: A case report

Introduction

Dropped head syndrome (DHS) is characterized by restricted active extension of the neck from a flexed position, and it can occur spontaneously or secondarily. ¹ This condition compromises quality of life due to impaired forward gaze, and the condition may result in the chin-on-chest deformity. This results in an increase in the risk of loss of balance and falls. ² Diagnosis is made based on the characteristic clinical findings of head droop.

MRI evaluation for DHS is now widely performed to exclude degenerative or neurological conditions, as well as assessing vertebral alignment and muscular abnormalities. Since early medical intervention is effective in most cases, accurate diagnosis is essential for appropriate treatment planning. However, there are a few reports presenting MRI evaluations in determining the causes of DHS.^2,3 Here, we present a case of DHS in which hypothyroid myopathy was suspected based on cervical spine MRI findings prior to other diagnostic tests. This study was conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained for anonymized patient information to be published in this article.

Case report

A 72-year-old female attended our hospital with a 1-year history of dropped head syndrome as her chief complaint. She had been diagnosed with bilateral carpal tunnel syndrome 3 years prior, following symptoms of numbness in both hands. She had no family history of neurological disease.

At the initial examination, the patient was alert and well-oriented, and she displayed neck weakness without evidence of limb paralysis. Laboratory tests showed elevated creatine kinase at 985 U/L. Cervical spine MRI showed a mild hyperintensity in the right paravertebral muscles on fat-suppressed T2-weighted images, as well as a reduced thyroid gland size and increased subcutaneous fat of the posterior neck (Figure 1). No significant degenerative changes were observed in the spinal canal. Suspecting hypothyroid myopathy, subsequent blood tests revealed thyroid-stimulating hormone levels of 98.9 μIU/mL and free thyroxine at 0.17 ng/dL, consistent with hypothyroidism. The thyroid microsomal antibodies were markedly high (6400 titer), while thyroglobulin antibodies were negative. No autoantibody indicative of focal myositis was detected. The patient’s medical history was unremarkable for thyroid disease, medication use, or iodine exposure.OPEN IN VIEWER

Needle electromyography of the trapezius and splenius capitis showed myopathic abnormalities, with low-amplitude, short-duration motor unit potentials on voluntary contraction, accompanied by fibrillations and positive sharp waves at rest. Repetitive nerve stimulation electromyography was within normal limits. From these electrophysiological tests, the probability of amyotrophic lateral sclerosis or myasthenia gravis decreased. Levothyroxine therapy was initiated, and after 4 months, the patient’s symptoms and laboratory findings significantly improved, with creatine kinase reduced to 72 U/L, thyroid-stimulating hormone to 1.50 μ IU/mL, and free thyroxine to 1.23 ng/dL. Follow-up needle electromyography showed improvement in myopathic changes. The response to treatment re-enforced the diagnosis of hypothyroid myopathy limited to the neck extensor muscles.

Post-treatment 24-month follow-up MRI revealed diffusely decreased volume of the paravertebral muscles (Figure 2). Hyperintensity of the right paravertebral muscles disappeared on the fat-suppressed T2-weighted image (Figure 2).OPEN IN VIEWER

Discussion

DHS results from various causes, such as neurological or neuromuscular conditions, inflammatory processes, metabolic disorders, and cervical spondylosis. ¹ According to a systematic review, endocrine disorders account for approximately 4% of DHS etiologies. ⁴ More common causes include isolated neck extensor myopathy (31.8%), Parkinson’s disease (20.2%), myasthenia gravis (12.4%), and amyotrophic lateral sclerosis (7.0%). ⁴ Imaging differential diagnosis is essential for early medical interventions in DHS because most of the conditions, including hypothyroid myopathy, are reversible.

Hypothyroid myopathy typically affects the proximal muscles of the extremities, but it can also present as DHS. ⁵ In our case, the patient presented with muscular symptoms localized to the cervical extensor on her first visit. Cervical spine MRI findings indicated hypothyroidism prior to the thyroid function tests. With the implementation of thyroid hormone replacement therapy, there was a notable improvement in the primary symptoms, blood test results, and needle electromyography findings. Furthermore, this patient exhibited carpal tunnel syndrome 3 years prior to the DHS. Carpal tunnel syndrome is well known as an early manifestation of hypothyroidism. ⁶ From this clinical course, we confirmed the diagnosis of cervical-extensor-limited myopathy due to hypothyroidism.

In typical cervical spine MRI protocols, we need to remember that the thyroid gland and subcutaneous fat are within the field of view together with the cervical musculoskeletal system. Sometimes, saturation pulses are utilized in the anterior area of the neck to prevent deterioration of cervical spine image quality due to motion artifacts. However, even in such cases, most part of the thyroid gland is usually imaged because of physiological cervical lordosis. As a characteristic feature of the thyroid gland, thyroid atrophy is reported in hypothyroid myopathy. ⁷ In our case, the thyroid gland atrophy on cervical spine MRI was indicative of hypothyroidism.

The MRI findings of hypothyroidism in musculoskeletal structure are rarely reported; however, enlargement of the gastrocnemius, deltoid, and trapezius muscles has been reported on high-signal intensity on T2-weighted images with contrast enhancement in the acute phase. ⁸ Ueshima et al. also reported high signals on short tau inversion recovery (STIR) images in the cervical extensor muscles, interspinous tissues, and anterior longitudinal ligament in patients with DHS and confirmed histologically the presence of necrosis and microvascular proliferation in skeletal muscles. ⁹ Mild high signals observed in the paravertebral muscles in our initial MRI may reflect those pathological findings.

In particular, chronic cases typically demonstrate degeneration and microvascular proliferation of ligaments. ¹⁰ Post-treatment follow-up MRI demonstrated a reduction in paraspinal muscle volume, corresponding to the resolution of abnormal muscle swelling related to hypothyroidism. The reduction, observed in our case, is similar to that in previous reports showing that thyroid replacement therapy may lead to subsidence of muscle hypertrophy in a type of hypothyroid myopathy called Hoffmann’s syndrome.^8,11 Radiologists should keep in mind that abnormal muscle swelling, similar to that seen in Hoffmann’s syndrome, may obscure the expected paraspinal muscle atrophy in DHS associated with uncontrolled hypothyroidism.

In conclusion, we report a case of hypothyroid myopathy related to DHS exhibiting thyroid atrophy, swelling, and abnormal signal intensity in the cervical extensor muscles on cervical spine MRI. In cervical spine MRI, we need to check the thyroid gland, as well as paravertebral muscles and subcutaneous fat, because the abnormal findings of these organs can provide clues to the diagnosis of underlying thyroid disease.