Q J Med 2003; 96: 455-457
© 2003 Association of Physicians
Correspondence |
Hashimoto’s encephalopathy: clinical, SPECT and neurophysiological data
Department of Neurology
Department of Nuclear Medicine
Sanjay Gandhi PGIMS
Lucknow
India
e-mail:
ukmisra{at}sgpgi.ac.in
ukmisra@indiatimes.com
Sir,
Hashimoto’s encephalopathy is a rare life- threatening medical emergency which manifests in patients suffering from chronic lymphocytic thyroiditis. The first case was described in 1966.1 It may present with subacute or acute encephalopathy, seizure, myoclonus, tremulousness, stroke-like episode, amnesia or dementia.2–6 Hashimoto’s encephalopathy should be considered if encephalopathy is associated with high level of thyroid microsomal antibodies, even in the absence of known thyroid disease. We would like to report some clinical, MRI, SPECT and EEG changes in a patient with Hashimoto’s encephalopathy.
A 42-year-old lady had suffered from behavioural abnormalities (irritability, restlessness and myoclonic jerks) for 2 years. The myoclonic jerks involved the extremities, 3–4 attacks per hour, were not associated with falling, and were absent during sleep. Four days before hospitalization, she developed progressive unsteadiness of gait and two attacks of generalized tonic-clonic seizures, each attack lasting for 2–3 min. Following seizure, she was febrile (38.9°C) and developed altered sensorium. There was no history of hypertension, diabetes mellitus or collagen vascular disease. No family member suffered from a similar illness.
On examination, the patient was well-built, her pulse was 100 bpm and regular, BP was 150/90 mmHg, temperature 38.9°C and respiratory rate 18 breaths/min. She was comatose, and her Glasgow coma scale score was 6. Pupils were normal size and reactive to light. Corneal reflex, Doll’s eye movement and gag reflex were present. There was no facial asymmetry. She moved all four limbs on painful stimuli. Muscle tone was increased in both upper and lower limbs. Biceps, triceps, knee and ankle reflexes were exaggerated and planters extensor bilaterally. Neck was supple. There was no hepatosplenomegaly and examinations of heart and lungs were normal. She had a diffuse goitre without any bruit.
Laboratory tests revealed total white blood cell count of 13 500/mm3 with 78% polymorphic, Hb 11 g%, ESR 57 mm for the first hour, and platelet counts 1.73 lac/mm3. Her fasting blood sugar was 100 mg/dl, BUN 18 mg/dl, serum creatinine 1 mg/dl, serum sodium 135 meq/l and serum potassium 3.5 meq/l. Serum calcium, alkaline phosphatase, serum proteins and urinalysis were normal. Radiograph of chest, electrocardiogram and cranial MRI were also normal. Cerebrospinal fluid revealed 49 mg/dl protein, 95 mg/dl sugar and no cells. Thyroid function test revealed T3 0.87 (normal = 1.3–2.8) mmol/l, T4 75.84 (normal = 60–160) mmol and TSH 4.17 (normal = 0.3–5.0) mmol. Thyroid microsomal antibody was present at 1/25 600 dilution. Electroencephalography on the fifth day of altered sensorium revealed diffuse theta to delta slowing without any right to left asymmetry. There was no epileptiform discharge. Her tibial somatosensory evoked potentials (right 16 ms, left 18 ms) and central motor conduction time to lower limbs (right 12.4 ms, left 12.6 ms) were normal. She was treated with intravenous antibiotics, sodium valproate 300 mg three times daily and hydrocortisone 100 mg intravenously 6-hourly, following which she made a remarkable recovery. On the fourth day of hydrocortisone therapy, she was conscious and conversed coherently. There was no recurrence of seizure and myoclonic jerks. She was prescribed oral prednisolone 40 mg daily, and sodium valproate continued.
Further investigation revealed absence of antinuclear antibody and antiparietal cell antibody. Fine-needle aspiration cytology of the thyroid swelling showed lymphocytic thyroiditis. Her P100 latency of visual evoked potentials were prolonged on both sides (right 112 ms, left 110 ms). A SPECT study carried out on third week revealed right temporoparietal hypoperfusion (Figure 1). Repeat EEG after 15 days of corticosteroid therapy was normal. She was discharged after 28 days of hospital stay. On discharge, her mini-mental scale score was 21 which was normal, as she was illiterate. Her pyramidal sign disappeared, and she could walk normally and perform all the activities of daily living.
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Our patient with Hashimoto’s encephalopathy presented with behavioural abnormality, myoclonus, generalized tonic-clonic seizure and altered sensorium. The diagnosis of Hashimoto’s encephalopathy was based on clinical features, thyroid microsomal antibody, FNAC of chronic lymphocytic thyroiditis and response to corticosteroid therapy. The presence of behavioural abnormality, myoclonic jerk, and walking difficulty in our patient simulated Cruetzfeldt-Jacob disease (CJD), but the EEG revealed diffuse slowing; in CJD, characteristic periodic discharges are seen. The dramatic improvement in clinical symptoms and normalization of EEG following corticosteroid further ruled out the possibility of CJD. In Hashimoto’s encephalopathy, various EEG abnormalities have been described which included diffuse slowing, mesial temporal lobe epileptic focus during ictus, diffuse slowing with triphasic discharge, and non-specific changes.8–10 The triphasic waves and background slowing in our patient normalized after 2 weeks of corticosteroid therapy, and the improved EEG was associated with improvement in the patient’s clinical condition. The exact pathophysiology of Hashimoto’s encephalopathy is unknown, but an autoimmune mechanism has been suggested because of its higher prevalence in females, fluctuating course, association with other autoimmune disorders and dramatic improvement following corticosteroid therapy.11 The focal and global cerebral symptoms may be attributed to autoimmune-mediated cerebral vasculitis, with or without immune complex deposition,7,12 and an anti-neuronal antibody-mediated mechanism.13 Vasculitis, if severe, may result in ischaemia or infarction which has been shown on CT scan or MRI studies.14 The cranial CT scan and MRI in our patient were normal, but SPECT revealed right temporoparietal hypoperfusion. This SPECT finding may suggest a low-flow area due to middle cerebral arterial vasculitis or postictal hypoperfusion, as our patient had two episodes of seizures. Previous SPECT studies in Hashimoto’s encephalopathy have shown global hypoperfusion or focal hypoperfusion, associated with focal abnormalities on CT scan.15,16
Visual evoked potential in our patient was prolonged and central motor and central sensory conduction time were normal. These abnormalities may also be explained by immunoinflammatory effect of Hashimoto’s encephalopathy resulting in ischaemic demyelination or axonal changes. Shaw et al. suggested that there may be a shared, yet unidentified antigen between the brain and thyroid gland, and it is possible that the same antibody is reactive against a common neuronal and thyroid antigen, resulting in thyroiditis and Hashimoto’s encephalopathy.12 Patients with Hashimoto’s thyroiditis are usually euthyroid. The diagnostic marker of Hashimoto’s encephalopathy is presence of thyroid microsomal antibody.
Hashimoto’s encephalopathy is a rare complication of Hashimoto’s thyroiditis, but should be considered in the differential diagnosis of patient presenting with encephalopathy and a CJD-like clinical picture, not least because of the therapeutic potential. Thyroid microsomal antibody is diagnostic, and corticosteroid therapy results in quick recovery.
Acknowledgments
We thank Rakesh Kumar Nigam for technical assistance.
References
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