AQUAPORIN-4 (AQP-4) IMMUNOGLOBULIN G SEROPOSITIVENEUROMYELITIS OPTICA: A REVIEW AND CASE REPORT

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C. Nwaze, Y. Eghwrudjakpor, N. Chinedu-Anunaso

Regions Stroke and Neuroscience Hospital, Owerri, Imo State, Nigeria.

Abstract

Background: Neuromyelitis optica spectrum disorder (NMOSD) is a relatively new terminology composed to encompass patients with neuromyelitis optica (NMO) and related immunological conditions. The diagnosis of this condition requires a seropositive aquaporin-4 immunoglobulin G (AQP-4 IgG), the presence of at least one core clinical characteristic and the exclusion of alternative diagnoses. Very few cases have been reported in sub-Saharan Africa.

Objective: The aim of this article is to report a classical case of NMOSD with AQP-4 IgG seropositivity and normal brain, cervical and thoracic MRI findings.

Result: We report a 25-year-old Nigerian woman who presented with recurrent and alternating weakness, pain and numbness of all limbs, associated with episodic painful left-sided tonic spasms and urinary incontinence. She had earlier had symptoms of recurrent, episodic and alternating loss of vision in both eyes, associated with ocular pain. Examination findings revealed an intact mental status, no cranial nerve deficit and no focal limb weakness. Right-sided deep tendon reflexes were exaggerated. Vital signs were within normal limits. Brain MRI, Cervical spine MRI and Thoracic spine MRI all revealed normal findings. Serum aquaporin-4 IgG assay returned positive with a titer of 1:32. She was commenced on high dose steroids and there was gradual improvement of symptoms.

Conclusion: These findings confirmed the diagnosis of neuromyelitis optica spectrum disorder, and satisfies the diagnostic criteria published in 2015 by the International Panel for NMO Diagnosis (IPND).

Keywords: Aquaporin, Neuromyelitis optica, Immunoglobulin

Introduction

Neuromyelitis Optica (NMO) is a rare, idiopathic, inflammatory and severe demyelinating disease of the central nervous system, primarily affecting the spinal cord and optic nerves.^1,2 First described in 1894 by Devic³, it is characterized by simultaneous or sequential loss of vision, associated with ocular pain, alongside spinal symptoms including symmetric paraplegia, sensory loss below the lesion and incontinence. These symptoms can occur in monophasic or relapsing courses.^2,4

Following the ground-breaking discovery of the relationship between neuromyelitis optica⁵ and the antibody AQP4-IgG a water channel protein, expressed in foot processes of astrocytes of the brain, spinal cord and optic nerve⁶, and other studies supporting this discovery ^7–10, AQP4-IgG was incorporated in the diagnostic criteria.¹¹ This was further modified with a new terminology known as Neuromyelitis Optica Spectrum Disorders (NMOSD) to encompass NMO and other CNS lesions which have similar immunopathogenesis and clinical behavior as NMO, and those which may possibly fulfil the NMO criteria in future.^2,11 The diagnostic criteria includes seropositive and seronegative divisions, with the seropositive division needing only one of six core clinical characteristics and the seronegative division requiring more stringent clinical features for diagnosis.¹ It is important to note that although NMOSD was formerly thought to be a severe variant of multiple sclerosis, recent clinical, immunopathogenic and radiological findings have proven that it is indeed a different entity.^5,10,12

NMOSD has been widely reported in developed countries. However, cases on the African continent have been quite limited. Some systematic reviews do not include any studies from Africa.¹³ There may also be significant under-reporting of available cases partly due to the limited access to MRI, AQP4-IgG testing, and other tests required for appropriate diagnosis. ¹⁴ Majority of cases reports in Africa originate from North Africa^15–17, with a few from Sub-Saharan Africa.^18–20 However, to the best of our knowledge, only one NMO AQP-IgG seropositive case has been reported in Nigeria.²¹ In this article, we report a young Nigerian lady with a classical presentation of neuromyelitis optica.