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We were delighted to read the article on orbital myositis heralding herpes zoster ophthalmicus (HZO) , highlighting the importance of considering an underlying infectious aetiology in cases of painful complex ophthalmoplegia.
Infections are a common cause of neurological complications in our setting, although unique cases continue to remind us about broader differentials. We encountered a case of a 55-year-old female with an unremarkable past medical history who was on holiday in Mombasa but presented to a local ophthalmologist with acute-onset diplopia and a painful swollen left eye. She was commenced on oral and topical antibiotics for a presumed pre-septal orbital cellulitis, but did not improve so was transferred urgently to our tertiary regional referral centre in Nairobi. Further social and travel history were non-revealing. On physical examination her blood pressure and temperature were normal, and she had no signs of thyroid disease. On full neurological examination she only had a left lateral rectus palsy with no other signs, and mild left peri-orbital swelling with erythema.
Comprehensive investigations (including metabolic, inflammatory, auto-immune, vasculitic and infective blood tests panels) as well as magnetic resonance imaging (MRI) of the brain with venography and angiography were all normal except for modestly raised C-reactive protein of 13 mg/dL (normal range 0-5). MRI of the orbits revealed enlargement of the left lateral rectus with...
Comprehensive investigations (including metabolic, inflammatory, auto-immune, vasculitic and infective blood tests panels) as well as magnetic resonance imaging (MRI) of the brain with venography and angiography were all normal except for modestly raised C-reactive protein of 13 mg/dL (normal range 0-5). MRI of the orbits revealed enlargement of the left lateral rectus with contrast enhancement. We diagnosed idiopathic orbital myositis (IOM) and commenced oral corticosteroids which resulted in marked improvement within 48 hours.
Our case highlights that IOM can present as orbital cellulitis , although the latter diagnosis is more serious and needs to be recognised and treated early. Ophthalmoplegia can be due to myositis of single or multiple extra-ocular muscles as our case and the HZO case illustrate, although there are reports of lateral rectus IOM occurring without any of the other signs of orbital inflammation . In the absence of other clinical and laboratory markers to support cellulitis, causes of orbital myositis need to be considered e.g. auto-immune disease, primary infections of the muscle including neuroborreliosis , or post-infectious sequelae even including after COVID-19 infection .
We hope our case adds further diagnostic considerations to those wonderfully illustrated by our colleague when confronted with a patient complaining of acute-onset painful diplopia.
 Chen T. Orbital myositis with herpes zoster ophthalmicus. Practical Neurology. Published Online First: 28 January 2021. doi: 10.1136/practneurol-2020-002870
 Lee NC, Loyal J, Berkwitt A. More Than Meets the Eye: Idiopathic Orbital Inflammation Mimicking Orbital Cellulitis. Cureus. 2021 Jan 12;13(1):e12655. doi: 10.7759/cureus.12655
 Wazir M, Faisal-Uddin M, Tambunan D, Jain AG. Idiopathic Lateral Rectus Myositis Without Signs of Orbital Inflammation. Cureus. 2019 Jun 7;11(6):e4859. doi: 10.7759/cureus.4859. PMID: 31410342; PMCID: PMC6684302.
 Mangan MS, Yildiz E. New Onset of Unilateral Orbital Myositis following Mild COVID-19 Infection. Ocular Immunology and Inflammation. Published Online First: 02 April 2021. doi: 10.1080/09273948.2021.1887282
 McNab AA. Orbital Myositis: A Comprehensive Review and Reclassification. Ophthalmic Plast Reconstr Surg, 2020; 36(2):109-117