Proposing a Neurotropic Etiology for Acute Posterior Multifocal Placoid Pigment Epitheliopathy and Relentless Placoid Chorioretinitis

PurposeTo reassess the underlying pathophysiology of acute posterior multifocal placoid pigment epitheliopathy (APMPPE) and relentless placoid chorioretinitis (RPC) through comparison with the non-inoculated eye of the von Szily animal model of neurotropic viral retinal infection.MethodsNarrative review.ResultsLiterature reports of isolated neurotropic viral entities and rising serological viral titers in APMPPE after presentation support a potential direct infective etiology. In general, viral transport along axons results in mitochondrial stasis and disruption of axoplasmic flow. Clinical manifestations of axoplasmic flow disruption in APMPPE/RPC may signify the passage of virus along the neuronal pathway. From a case series of 11 patients, we demonstrate a timely, spatial, and proportional association of optic disc swelling with APMPPE lesion occurrence. Signs within the inner retina appear to precede outer retinal lesions; and acute areas of outer nuclear layer (ONL) hyperreflectivity appear to be the result of coalescence of multiple hyperreflective foci resembling axonal spheroids (which occur as a consequence of axoplasmic disruption) and follow the Henle fiber layer neurons. Underlying areas of retinal pigment epithelium (RPE) hyper-autofluorescence follow ONL hyperreflectivity and may signify localized infection. Areas of apparent choriocapillaris hypoperfusion mirror areas of RPE/Bruch’s membrane separation and appear secondary to tractional forces above. Increases in choroidal thickness with lesion occurrence and focal areas of choriocapillaris hypoperfusion are observed in both APMPPE/RPC and the von Szily model.ConclusionsThe neurotrophic infection model provides significant advantages over the existing primary choriocapillaris ischemia hypothesis to account for the range of imaging signs observed in APMPPE and RPC.

Recent Advances in Basic Research for CSF1R-Microglial Encephalopathy

Colony-stimulating factor-1 receptor-microglial encephalopathy is a rare rapidly progressive dementia resulting from colony-stimulating factor-1 receptor (CSF1R) mutations, also named pigmentary orthochromatic leukodystrophy (POLD), hereditary diffuse leukoencephalopathy with spheroids (HDLS), adult-onset leukoencephalopathy with axonal spheroids, and pigmented glia (ALSP) and CSF1R-related leukoencephalopathy. CSF1R is primarily expressed in microglia and mutations normally directly lead to changes in microglial number and function. Many animal models have been constructed to explore pathogenic mechanisms and potential therapeutic strategies, including zebrafish, mice, and rat models which are with CSF1R monogenic mutation, biallelic or tri-allelic deletion, or CSF1R-null. Although there is no cure for patients with CSF1R-microglial encephalopathy, microglial replacement therapy has become a topical research area. This review summarizes CSF1R-related pathogenetic mutation sites and mechanisms, especially the feasibility of the microglia-original immunotherapy.

Heterogeneous immunoreactivity of axonal spheroids in focal symmetrical encephalomalacia produced by Clostridium perfringens type D epsilon toxin in sheep

Since axonal injury (AI) is an important component of many veterinary neurologic disorders, we assessed the relative ability of a panel of antibodies (amyloid precursor protein, 3 subunits of neurofilament protein, protein gene product 9.5, ubiquitin, and synaptophysin) to detect axonal swellings or spheroids. Abundant axonal spheroids found in necrotic internal capsule foci produced in 4 sheep by chronic Clostridium perfringens type D epsilon neurotoxicity provided a model system in which to evaluate this important diagnostic tool. There was heterogeneous labeling of subsets of spheroids by the respective antibodies, suggesting that, in order to detect the complete spectrum of AI in diagnostic cases, a range of antibodies should be used, not only when spheroids are plentiful but also when they are few in number or incompletely developed. The application of insufficient markers in the latter cases can potentially lead to the contribution of AI to lesion pathogenesis being underappreciated.

Insights Into the Role of CSF1R in the Central Nervous System and Neurological Disorders

The colony-stimulating factor 1 receptor (CSF1R) is a key tyrosine kinase transmembrane receptor modulating microglial homeostasis, neurogenesis, and neuronal survival in the central nervous system (CNS). CSF1R, which can be proteolytically cleaved into a soluble ectodomain and an intracellular protein fragment, supports the survival of myeloid cells upon activation by two ligands, colony stimulating factor 1 and interleukin 34. CSF1R loss-of-function mutations are the major cause of adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) and its dysfunction has also been implicated in other neurodegenerative disorders including Alzheimer’s disease (AD). Here, we review the physiological functions of CSF1R in the CNS and its pathological effects in neurological disorders including ALSP, AD, frontotemporal dementia and multiple sclerosis. Understanding the pathophysiology of CSF1R is critical for developing targeted therapies for related neurological diseases.

Progressive Asymmetrical Limb Impairment and Cognitive Decline With Leukoencephalopathy

A 41-year-old man sought care for progressive left-sided impairment over many months consistent with progressive left hemiapraxia and left hemiparesis and cognitive decline. He also exhibited features of the alien limb phenomenon, with the left arm grabbing things involuntarily. He had no prior medical disorders and no family history of significant neurologic disorders. Initial evaluations with brain magnetic resonance imaging showed evidence of bilateral, asymmetrical, severe white matter abnormalities, right greater than left hemisphere. There was no gadolinium enhancement. Cervical and thoracic spine magnetic resonance imaging findings were normal. The magnetic resonance imaging white matter abnormalities progressed over serial imaging. Cerebrospinal fluid assessment was normal except for increased neuron-specific enolase value, without increased white blood cells, immunoglobulin G index, or unique cerebrospinal fluid oligoclonal bands. A brain biopsy of the right hemispheric white matter showed marked axonal spheroids on hematoxylin and eosin staining, as well as on electron microscopy. A diagnosis of sporadic, adult-onset, diffuse leukoencephalopathy with axonal spheroids was made. There are no known treatments for diffuse leukoencephalopathy with axonal spheroids. Treatment is symptomatic only, directed by physical medicine and rehabilitation experts and cognitive experts. Continued rapid worsening of the patient’s ambulatory dysfunction over months required increasing use of gait aids, including a cane and wheelchair. He had development of neurogenic bladder dysfunction and pseudobulbar-associated emotional incontinence. His condition progressed leading to death 29 months after onset of his neurologic dysfunction. This case patient had common features of sporadic, adult-onset, diffuse leukoencephalopathy with axonal spheroids, with progressive neurologic degeneration typically over months to a few years, often with substantial asymmetry in presentation.