Moyamoya disease is a progressive cerebrovascular disorder involving stenosis or occlusion of distal internal carotid arteries (ICA) and proximal middle cerebral arteries (MCA), with the formation of fragile collateral vessels that resemble a “puff of smoke” on angiography [2] [3] . Although idiopathic in most cases, Moyamoya can be associated with conditions like Down syndrome and neurofibromatosis type 1 [4] .

Cerebral vasculitis encompasses a range of disorders characterized by inflammation of cerebral vessels. It may be primary or secondary to systemic conditions, including autoimmune diseases and infections [5] . Imaging differentiation is crucial due to overlapping features between Moyamoya disease and vasculitis. In a comparative study by Kraemer and Berlit (2010), conventional angiography diagnosed all Moyamoya cases but only 76.5% of vasculitis cases, illustrating the diagnostic complexity [6] .

Misdiagnosis is common. Graf et al. (2019) found that in 192 Caucasian patients with Moyamoya angiopathy (MMA), 62% were initially misdiagnosed, with vasculitis being the most common incorrect diagnosis (31%) [7] . Vessel wall MRI (VW-MRI) improves diagnostic precision, with concentric enhancement suggesting vasculitis and absent enhancement in classic Moyamoya [8] .

This report describes a diagnostic challenge in a patient with isolated UMN facial palsy. Initial imaging suggested Moyamoya, but subsequent findings and expert review led to a final diagnosis of cerebral vasculitis.

An Australian Caucasian woman in her 30 s presented to a regional hospital with acute onset of right facial drooping. She denied limb weakness, speech disturbance, headache, visual changes, or systemic symptoms. Past history included hypertension and pancreatitis. Family history was notable for cerebrovascular disease in multiple first-degree relatives. She was a non-smoker with no recent infections or medication changes.

On neurological examination, there was isolated right UMN facial palsy—evident by lower facial weakness with preserved forehead movement. Muscle strength, reflexes, cerebellar function, and other cranial nerves were intact. No sensory deficits were identified.

CT brain was unremarkable. CTA revealed small calibre distal ICA and MCA with prominent meningeal vessels, suggestive of Moyamoya disease. On Day 2, MRA (time-of-flight sequence) showed beading of the M1-M2 segments of the right MCA and scattered irregularities in anterior and posterior cerebral arteries without significant stenosis ( Figure 1 ). These findings were more consistent with cerebral vasculitis.

Inflammatory markers included ESR 20 mm/h and a borderline ANA (1:40). ANCA, anti-dsDNA, ENA, antiphospholipid antibodies, and lupus anticoagulant were all negative. CSF analysis and brain biopsy were not performed due to low suspicion of systemic disease and patient preference.

Three neuroradiologists independently and blindly reviewed the imaging, confirming the findings supported cerebral vasculitis over Moyamoya disease.

The patient was initially started on aspirin for presumed ischemic etiology. Following tertiary review and revised diagnosis, aspirin was discontinued. Amitriptyline was initiated for persistent retro-orbital and occipital neuralgia. No immunosuppressive therapy was commenced due to isolated presentation and improving symptoms.

Over the following four months, the patient reported 95% improvement in facial weakness. She experienced occasional episodes of transient blurred vision and persistent neuralgia but no new neurological deficits. She remains under follow-up with neurology and neuroradiology teams to monitor disease course and imaging progression.

This case presents a rare diagnostic dilemma of distinguishing cerebral vasculitis from Moyamoya disease in a patient with isolated UMN facial palsy ( Table 1 ). Moyamoya disease typically shows bilateral stenosis with collateral formation, while vasculitis exhibits segmental beading without extensive collateralisation [9] . In this case, the absence of bilateral findings and presence of vessel irregularities without occlusion or collaterals favored vasculitis.

Three independent neuroradiologist reviews supported the vasculitis diagnosis. Similar diagnostic confusions have been reported [6] [7] [10] . VW-MRI could further support diagnosis but was not available in this case.

UMN facial palsy usually suggests a central lesion (stroke, tumour), and isolated presentation is rare. Focal small-vessel inflammation might explain the selective involvement seen here.

The absence of CSF or biopsy is a limitation, though clinical improvement and imaging supported a working diagnosis. This case underscores the utility of MRA, multidisciplinary evaluation, and caution against premature diagnoses in young patients with neurovascular symptoms [11] .

Patient Perspective: “It’s been an interesting journey. As someone from a medical background, I initially thought it was Bell’s palsy. Being told it might be Moyamoya was terrifying. When they later diagnosed vasculitis, it was a relief but also raised many questions. I’m still dealing with pain and uncertainty, but I appreciate the thoroughness of the team in pursuing the correct diagnosis. The experience has taught me the importance of second opinions and not settling for the first explanation—especially when something doesn’t feel right. While some symptoms linger, I feel reassured knowing I’m under continuous care and monitoring.”

Written informed consent was obtained from the patient in accordance with the journal’s ethical standards and the CARE (CAse REport) guidelines for case reports. Informed consent was obtained from the patient for publication of this case report and the included images.