Autoimmune hypophysitis: Anesthetic implications.

Sir,

Autoimmune disease of the pituitary is rare and poorly understood as a pathologic entity.[1] The purpose of reporting this case is the rarity of the disease, especially in males, and scarce literature on such patients presenting for other than transphenoid surgery for autoimmune hypophysitis (AH).

An 80 kg, 60-year-old man was scheduled for fractured tibia surgery. One year ago, the patient had presented with headache, vomiting, delirium, and incoherent speech and was diagnosed to have AH with central hypothyroidism and hypocortisolism. MRI brain revealed an intrasellar enhancing lesion with thick nontapering stalk and enhancement of adjacent dura suggestive of hypophysitis [Figure 1]. Patient had responded to high doses of steroids (prednisolone 20 mg three times a day) [Figure 2]. Presently, he was on prednisolone 2.5 mg once a day and thyroxine 100 mcg. Preoperative biochemical investigations including thyroid function tests, electrocardiogram, X-ray chest, and 2D echocardiography were within normal limits.

Figure 1

(a) MRI brain coronal section showing intrasellar enhancing lesion with thick nontapering stalk and enhancement of adjacent dura suggestive of hypophysitis or macroadenoma. (b) MRI brain sagittal section showing intrasellar enhancing lesion with thick nontapering stalk and enhancement of adjacent dura suggestive of hypophysitis or macroadenoma

Figure 2

MRI coronal section post-treatment showing shrunken and flattened anterior pituitary giving empty sella appearance

Patient received his morning dose of thyroxin and prednisolone. Intravenous (IV) infusion of Ringer's lactate was started and 100 mg hydrocortisone was given. Routine monitors were attached. Combined spinal epidural anesthesia was administered by injection of 3.2 ml 0.5% heavy bupivacaine with 1 mg of preservative free midazolam into the subarachnoid space. Sensory loss was achieved up to T8 level. Patient did not require epidural supplementation as surgery lasted for one and half hours. Patient was hemodynamically stable all throughout the procedure. 2 L of crystalloid was administered IV perioperatively. Postoperative analgesia was administered using epidural top ups of tramadol. Hydrocortisone 100 mg IV 6 hourly was administered till his oral medication was restarted. Recovery was uneventful and patient was discharged on the 8th postoperative day.

AH or lymphocytic hypophysitis is defined as below normal production of one or more hormones due to pituitary gland dysfunction of autoimmune origin. The estimated incidence of AH is one in nine million per year[1] with a higher prevalence among females.[2] The autoimmune destruction may take 12–40 years to produce symptoms. The gland initially enlarges and is edematous, which results in pressure on adjacent structures causing headache, visual disturbances, etc.[34] Subsequently, there is atrophy and destruction of the gland. Adrenocorticotropin releasing hormone (ACTH) deficit is usually the earliest and most frequent hormonal impairment. Our patient presented with hypothyroidism and hypocortisolism. Surgery is one of the most potent activators of the hypothalamic pituitary adrenal (HPA) axis. Cortisol releasing hormone (CRH), ACTH, and cortisol levels increase significantly in patients with an intact normally functioning HPA axis, during surgery and anesthesia. This response is absent in patients with AH and they can have adrenal crisis intraoperatively.[5]

Regional anesthesia is preferred in this group of patients whenever possible, while ensuring adequate hormonal supplementation and maintenance of intravascular fluid volume to prevent an acute hypotensive crisis. Patients need vigilant monitoring for cardiovascular instability.[5] Regional anesthesia with moderate doses of local anesthetic can to some extent prevent perioperative crisis due to reduction of stress response. However, amide local anesthetic metabolism is slow predisposing to systemic toxicity due to hypothyroidism. All drugs must be administered carefully to avoid myxedema coma.