PACNS is a rare disorder that can present with virtually any neurological sign and has variable findings on neuroimaging.1
The inconsistent presentation often makes the diagnosis elusive. By definition, the vasculitis is isolated to the CNS.2
Secondary causes of vasculiitis must be excluded with a thorough clinical and laboratory evaulation.3
This disorder was initially termed Isolated Central Nervous System Vasculitis in the 1950s. Since that time, the aetiology of the disorder has not been clearly elucidated. A viral aetiology has been suggested but the diagnosis is still one of exclusion.4 5 6
Making the diagnosis in a timely manner is crucial because this disorder is invariably fatal if left untreated.7
MRI and CT scans are often helpful in the initial investigation, but further evaluation is needed to make a diagnosis. Neuroimaging in PACNS can often mimic other disease processes such as neoplasm, intracranial haemorrhage and demyelinating disorders.8
There have even been several case reports of patients with normal neuroimaging.9
Angiography is the imaging modality of choice. However, this modality is still somewhat limited because the disease affects the small and medium sized vessels and may not be well visualised.2
The gold standard to diagnose PACNS is histopathology.10
The histopathology of CNS angiitis has been well-described. The inflammation associated with the disease is granulomatous in nature. Macrophages, lymphocytes and multinucleated giant cells are often found in the affected arteries and arterioles. In several case studies, the pathological findings are similar to those found in patients with Takayasu arteritis and giant cell arteritis.10
Ischaemia and/or infarction appear to be common in affected patients. While the majority of cases appear to affect the cerebral cortex more than the subcortical regions, our patient's lesions involved the subcortical vessels as well. H&E sections demonstrate widespread involvement of the cerebral arterioles by a mixed lymphocytic, mildly plasmacytic, vasculitis with focal necrosis of vessel walls and thrombosis with accompanying areas of ischaemic necrosis.
Treatment of this disease has significantly improved over the past 50 years. When the disorder was first described in the 1950s it was uniformly fatal.8
It was not until several years later that the combination of cyclophosphamide and steroids yielded effective treatment results. Since the introduction of the two-drug regimen, most patients have responded well to treatment. The treatment duration ranges between 6 months and 1 year depending on clinical response. Close follow-up and serial neuroimaging is required to assess response to treatment.
While PACNS has been recognised since the 1950s, its variable presentation has confounded clinicians and radiologists for decades. The clinician must have a high clinical suspicion for this disease when a patient presents with neurological manifestations not explained by another disease process. MRI and CT scans can aid in developing a differential diagnosis, but neuroimaging should include angiography. Biopsy is often essential in making the diagnosis. Before a diagnosis of PACNS can be made, an exhaustive search should be undertaken to rule out other treatable causes of the vasculitis. Treatment should be initiated as soon as possible. Most patients tolerate treatment well and experience full recovery. Unfortunately, in many patients the diagnosis of PACNS is made postmortem. Hospital team members often encounter new-onset seizure and CNS lesions. It is important for us to keep a broad differential and aggressively pursue definitive diagnosis.
- CNS angiitis is a diagnosis of exclusion.
- Biopsy is often necessary for definitive diagnosis.
- CNS angiitis is treatable if diagnosed early but fatal if left untreated.
- Monitor patients closely for side effects of immunosuppressive treatment.