Isolated sixth nerve palsy: an unusual manifestation of preeclampsia

Dear Editor:

Preeclampsia is a pregnancy complication of unknown aetiology with an estimated frequency of 2%–8%. It is characterised by hypertension after week 20 of gestation in women with previously normal blood pressure, together with proteinuria, or in the absence of proteinuria but with presence of thrombocytopaenia, kidney failure, altered liver function, pulmonary oedema, or neurological symptoms.¹ The most frequent neurological symptoms include headache and visual alterations, with isolated oculomotor palsy being exceptional.² We present the case of a primiparous woman (37 weeks pregnant) whose first neurological symptom of preeclampsia was sixth nerve palsy; we also assess the possible action mechanisms.

Our patient was a 31-year-old woman assessed in the emergency department due to progressive onset of binocular diplopia in the horizontal plane, with no headache, fever, or other focal neurological signs. The neuro-ophthalmological evaluation revealed 20/20 Snellen visual acuity in both eyes, and the eye fundus examination showed well-defined papillae and spontaneous venous pulsation; the confrontation visual field test yielded normal results; esotropia was observed in the primary gaze position with slightly impaired adduction of the left eye. No other neurological alterations were observed. The general examination detected no fever, blood pressure values of 150/90 mm Hg, and distal oedema in both lower limbs; a blood analysis revealed thrombocytopaenia with 100 000 platelets/μL, increased LDH levels (418 IU/L), and proteinuria (Table 1). In view of these symptoms, and considering the diagnosis of preeclampsia and findings suggestive of isolated sixth nerve palsy, we requested an MRI study before labour was induced. The MRI study ruled out an underlying intracranial lesion, and labour was induced 24 hours after the patient's admission to hospital; a healthy baby was born with no complications. After delivery, the patient presented normal blood pressure values and diplopia progressively improved, fully resolving in 48 hours.

Table 1.

Blood test at admission.

Peripheral blood		Biochemical study				Urine analysis
Haemoglobin	11.6 g/dL	Total protein	5 g/dL	Lactate dehydrogenase	418 IU/L	Protein++
Haematocrit	56.2%	Albumin	2.7 g/dL	GOT	9 IU/L
MCV	85.0 fL	Urea	12 mg/dL	GPT	13 IU/L
				Glucose	95 mg/dL
Platelets	10 × 10^4/μL	Creatinine	0.9 mg/dL
ESR	20 mm/h	Uric acid	6.7 mg/dL
Leukocytes	14 380/μL	Alkaline phosphatase	110 IU/L

ESR: erythrocyte sedimentation rate; GOT: glutamic oxaloacetic transaminase; GPT: glutamate-pyruvate transaminase; MCV: mean corpuscular volume.

Isolated sixth nerve or abducens nerve palsy during pregnancy is exceptional, although isolated cases have been reported.^3–6 The action mechanism by which preeclampsia causes neuropathy remains unknown, although the absence of other findings and previous published data in the literature suggest that it may cause vasospasm of the vasa nervorum, causing transient ischaemia that would lead to nerve palsy.⁶ In our patient, who had no history suggesting an underlying systemic disease, presenting preeclampsia and no fever, intracranial hypertension, or underlying intracranial lesion on MR images, together with the complete resolution of symptoms postpartum, suggest preeclampsia-related sixth nerve palsy.