Acute Flaccid Quadriplegic Myopathy and Encephalopathy with Extensive Muscle Magnetic Resonance Imaging Changes in Thyroid Storm

Abstract

Thyroid storm (TS) is a rare hyperthyroidism associated multisystem decompensation and can mimic a systemic inflammatory response syndrome. It is diagnosed in the presence of fever with cardiovascular, central nervous system, and gastrointestinal complications. Only a few reports of acute flaccid quadriplegic thyrotoxic myopathy (TM) with TS have been reported. However, muscle magnetic resonance imaging (MRI) findings in TM have not been yet been reported. Our patient underwent muscle MRI and showed some unusual features. These are discussed in this article.

INTRODUCTION

Thyroid storm or thyrotoxic storm (TS) is a multisystem decompensation seen in the context of hyperthyroidism. It is usually precipitated by stress. TS is characterized by four features: fever, sinus tachycardia or supraventricular arrhythmias, neurological symptoms (agitation, confusion, delirium, or coma), or gastrointestinal symptoms (vomiting, diarrhea, or intestinal obstruction).

Hyperthyroidism is known to be associated with a chronic proximal myopathy, myasthenia gravis, thyrotoxic periodic paralysis, thyroid ophthalmopathy, or a polyneuropathy.[1] Although rhabdomyolysis and flaccid quadriplegia with TS have been noted, muscle magnetic resonance imaging (MRI) findings have not yet been described.[2,3,4,5,6] Only one case of thyrotoxic myopathy (TM) with muscle stiffness reportedly showed bilateral biceps femoris atrophy on MRI.[7]

CASE REPORT

A 73-year-old male was admitted with fever of 2-week duration and altered sensorium of 1-day duration. Three days before admission, he developed severe low backache, generalized weakness, decreased appetite, recurrent fever, and disorientation. He had a long-standing history of type 2 diabetes mellitus, systemic hypertension, and coronary artery disease. He had no history of thyroid disease, goiter, or muscle weakness. On examination, he was febrile, drowsy, agitated (encephalopathic), and tachycardic without any focal neurological deficits. An encephalitic syndrome was considered, and he was intubated and mechanically ventilated. EEG showed triphasic waves. Serum NH3, dengue IgM, leptospiral IgM, Weil–Felix test, febrile screen, serum amylase, lipase, urine porphobilinogen, blood and urine cultures, N-methyl-D-aspartate, voltage-gated potassium channels, and paraneoplastic antibodies, and cerebrospinal fluid study was normal.

Thyroid function tests were abnormal (free T3: >7.7 ng/ml, free T4: 23.96 pg/ml, and thyroid-stimulating hormone: < 0.001 μIU/mL. A diagnosis of thyrotoxic storm (TS) was made after consulting endocrinology. He was started on cold intravenous (IV) fluids, cooling blankets, IV paracetamol, injection hydrocortisone 100 mg IV thrice daily, tablet propylthiouracil 400 mg Q6H, after a 1000 mg loading dose, Lugol's solution 10 drops BD, and propranolol 40 mg q6 h. He also required noradrenaline and vasopressin for inotropic support. Meropenem and azithromycin were also started. Dexmedetomidine was started for agitation. Neuromuscular blockers were not used. Paroxysmal atrial fibrillation was noted and was reverted with amiodarone.

A calculated Burch–Wartofsky score was 135 suggestive of TS. Insulin infusion was started to maintain glucose between 140 and 180 mg/dl. Fluid intake was maintained above 2.5 L.

On day 3, he was noted to have flaccid areflexic quadriparesis and mild bifacial weakness with weaning difficulty. A Medical Research Council sum score was 30.

MRI brain and spine were normal. Nerve conduction study showed reduced compound muscle action potential amplitudes with normal sensory nerve action potentials. On day 3 after admission, electromyography (EMG) study showed myopathic potentials, early recruitment, and profuse denervation potentials (fibrillations and positive sharp waves) in the upper and lower limb muscles. CPK levels were 600 u/l. A whole-body muscle MRI showed extensive short tau inversion recovery (STIR) sequence muscle hyperintensities involving the paraspinal muscles, gluteal, pelvic, thigh, and calf muscles was done concurrently as part of our departmental protocol for acute flaccid weakness [Figure 1]. Only a limited study could be done due to patient uncooperativeness. A diagnosis of TS with an acute TM and encephalopathy was made. After a week, his thyroid function tests normalized and Neomercazole was started through nasogastric tube. On day 15, he was tracheostomized. Ultrasound showed bilateral pleural effusion and a right hemidiaphragm elevation. His sensorium gradually improved, and on day 40, his tracheostomy was closed. The patient was unwilling for a muscle biopsy. His muscle power improved to Grade 4/5 in the limbs and he was able to sit up in a chair. He was discharged to domiciliary care. However, he continued to have medical complications and expired after 2 months.

Figure 1.

(a-c) Coronal short tau inversion recovery images. (a) Diffuse hyperintensities in the thigh, calf, and shoulder girdle muscles. Scattered subcutaneous hyperintensities are also seen. (b) Muscle hyperintensities in the paraspinal muscles and hamstrings. (c) Muscle hyperintensities in the gluteal muscles. (d) Sagittal lumbosacral spine (LS) spine images showing lumbar paraspinal muscle hyperintensity and subcutaneous fluid collection

DISCUSSION

Neuromuscular disorders (NMDs) in hyperthyroidism include TM, periodic paralysis, myasthenia gravis, or a thyrotoxic polyneuropathy.[8,9] However, there is a scarcity of reports in TS, and acute NMD complications are usually related to hypokalemic periodic paralysis, myasthenia gravis, or an acute bulbar myopathy.[10,11] Acute flaccid quadriparesis (AFP) in TS is uncommon.[5,12,13]

Thyrotoxicosis causes a myopathy due to perturbations of oxidative phosphorylation, lysosomal activity, protein synthesis, myosin chain structure, and metabolism. Thyroid hormones increase cyclic adenosine monophosphate activity resulting in a hypermetabolic condition. AFP in this setting has a grim prognosis and may require months of rehabilitation for recovery. We cannot completely exclude the possibility of a critical illness myopathy (CIM) in our patient; however, the early denervation potentials in the EMG (appearing by day 3 after admission) suggest a thyroid myopathy which probably predated the admission and subsequently exacerbated during the TS. In CIM, denervation potentials on EMG take a few more days to appear (on average 7–10 days).[14]

CONCLUSION

Our patient displayed severe generalized muscle hyperintensities on MRI STIR imaging, predominantly in the large muscles of the lower limbs and the paraspinal muscles. The differential diagnosis of muscle hyperintensities on STIR MRI includes inflammatory, infectious (viral myositis), traumatic, denervation secondary to polyneuropathy, rhabdomyolysis, and muscle infarction. However, the diagnosis was narrowed down by the clinical presentation and the diffuse nature of hyperintensities as conditions such as infarction present with localized changes. In conclusion, we present a rare case of AFP with myopathy due to a TS, with extensive muscle changes on MRI. MRI STIR imaging of muscles is a useful adjunctive investigation in patients with AFP.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.