Leptomeningeal familial amyloidosis: A rare differential diagnosis of leptomeningeal enhancement in MRI

Clinical considerations in early-onset cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is an important cerebral small vessel disease associated with brain haemorrhage and cognitive change. The commonest form, sporadic amyloid-β CAA, usually affects people in mid- to later life. However, early-onset forms, though uncommon, are increasingly recognized and may result from genetic or iatrogenic causes that warrant specific and focused investigation and management. In this review, we firstly describe the causes of early-onset CAA, including monogenic causes of amyloid-β CAA (APP missense mutations and copy number variants; mutations of PSEN1 and PSEN2) and non-amyloid-β CAA (associated with ITM2B, CST3, GSN, PRNP and TTR mutations), and other unusual sporadic and acquired causes including the newly-recognized iatrogenic subtype. We then provide a structured approach for investigating early-onset CAA, and highlight important management considerations. Improving awareness of these unusual forms of CAA amongst healthcare professionals is essential for facilitating their prompt diagnosis, and an understanding of their underlying pathophysiology may have implications for more common, late-onset, forms of the disease.

Current Review of Leptomeningeal Amyloidosis Associated With Transthyretin Mutations

INTRODUCTION

Leptomeningeal amyloidosis (LA) represents a rare subtype of familial transthyretin (TTR) amyloidosis, characterized by deposition of amyloid in cranial and spinal leptomeninges. Of >120 TTR mutations identified, few have been associated with LA.

CASE REPORT

A 27-year-old male presented with a 2-year history of progressive symptoms including cognitive decline and right-sided weakness and numbness. Cerebrospinal fluid (CSF) analyses demonstrated high protein level. Gadolinium-enhanced magnetic resonance imaging (MRI) revealed extensive leptomeningeal enhancement over the surface of the brain and spinal cord. Pathologic analyses revealed a TTR mutation c.113A>G (p.D38G).

REVIEW SUMMARY

Fifteen mutations and genotype-phenotype correlation of 72 LA patients have been summarized to provide an overview of LA associated with transthyretin mutations. The mean age of clinical onset was 44.9 years and the neurological symptoms primarily included cognitive impairment, headache, ataxia seizures and hearing, visual loss. CSF analysis showed elevated high CSF protein level and MRI revealed extensive leptomeningeal enhancement.

CONCLUSION

Clinicians should be aware of this rare form of familial transthyretin amyloidosis as well as its typical MRI enhancement and high CSF protein. The important role of biopsy, genetic testing and the potential early diagnosis value of contrast MRI were suggested. Early recognition of these characteristics is important to provide misdiagnosis and shorten the time before correct diagnosis. These findings expand the phenotypic spectrum of TTR gene and have implications for the diagnosis, treatment, and systematic study of LA.

Histone-mutant glioma presenting as diffuse leptomeningeal disease

Glioblastoma multiforme is the most common malignant primary brain tumor in adults. Histone H3 mutations have been identified in pediatric and adult gliomas, with H3K27M mutations typically associated with a posterior fossa midline tumor location and poor prognosis. Leptomeningeal disease is a known complication of histone-mutant glioma, but uncommon at the time of initial diagnosis. We describe a case of glioblastoma with H3K27M mutation that initially presented with progressive vision loss due to diffuse leptomeningeal disease in the absence of a mass lesion other than a small cerebellar area of enhancement and with cerebrospinal fluid cytology negative for malignant cells on two occasions, highlighting the importance of including primary CNS malignancies in the differential of diffuse radiographic leptomeningeal enhancement.

Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor in adults. Histones are molecules around which DNA winds. GBM and other gliomas sometimes have genetic alterations called mutations in histone genes. Of these, a specific alteration in histone 3 called H3K27M has been described in a variety of primary brain tumors. In adult gliomas, the H3K27M mutation is typically associated with tumors located within the brainstem or other structures in the midline of the central nervous system and a poor prognosis. Although previously reported, involvement of the leptomeninges (the thin membranes covering the brain and spinal cord) is uncommon at the time of initial diagnosis of gliomas harboring H3K27M mutations. We describe a case of GBM that initially presented with vision loss due to diffuse leptomeningeal involvement. Imaging and laboratory studies, including two cerebrospinal fluid analyses by lumbar puncture, did not establish a diagnosis. Brain biopsy confirmed the presence of a tumor, and genetic testing performed on the tumor tissue identified the histone mutation. This case highlights the importance of including primary central nervous system malignancies as a possible diagnosis when there is diffuse radiographic leptomeningeal enhancement.

Circumferential intrathecal ossification in oculoleptomeningeal amyloidosis

Oculoleptomeningeal amyloidosis (OLMA) is a variant of familial amyloidosis that results in amyloid deposition in the vitreous and leptomeninges. A 60-year-old woman with a history of OLMA presented to the emergency department for obtundation secondary to apparent shunt malfunction and lower extremity weakness. CT imaging of her spinal axis showed high attenuation material present intradurally from the mid cervical level extending through the thoracic and lumbar spine in the extramedullary space. MRI demonstrated circumferential signal enhancement surrounding the entire spinal cord. The patient underwent open biopsy at L3-L5. Upon opening the dura, a homogenous intradural ossification encasing the nerve roots was seen. Given the extent of the ossification, no further attempt at decompression was performed. Microscopic review of the biopsy sample revealed sclerotic bone with focal amorphous material consistent with amyloid. To our knowledge this is the first case report of a patient with OLMA presenting with extensive circumferential intrathecal ossification from amyloid deposition. Despite examples of leptomeningeal enhancement in patients with OLMA, extensive intradural ossification is a finding that has not been previously reported radiographically or post mortem.

Oculoleptomeningeal Amyloidosis associated with transthyretin Leu12Pro in an African patient

Oculoleptomeningeal amyloidosis is a rare manifestation of hereditary transthyretin (TTR) amyloidosis. Here, we present the first case of leptomeningeal amyloidosis associated with the TTR variant Leu12Pro mutation in an African patient. A 43-year-old right-handed Nigerian man was referred to our centre with rapidly progressive neurological decline. He presented initially with weight loss, confusion, fatigue, and urinary and erectile dysfunction. He then suffered recurrent episodes of slurred speech with right-sided weakness. He went on to develop hearing difficulties and painless paraesthesia. Neurological examination revealed horizontal gaze-evoked nystagmus, brisk jaw jerk, increased tone, brisk reflexes throughout and bilateral heel-shin ataxia. Magnetic resonance imaging showed extensive leptomeningeal enhancement. Cerebrospinal fluid analysis showed a raised protein of 6.4 g/dl. Nerve conduction studies showed an axonal neuropathy. Echocardiography was characteristic of cardiac amyloid. TTR gene sequencing showed that he was heterozygous for the leucine 12 proline mutation. Meningeal and brain biopsy confirmed widespread amyloid angiopathy. TTR amyloidosis is a rare cause of leptomeningeal enhancement, but should be considered if there is evidence of peripheral or autonomic neuropathy with cardiac or ocular involvement. The relationship between different TTR mutations and clinical phenotype, disease course, and response to treatment remains unclear.

Subarachnoid hemosiderosis and superficial cortical hemosiderosis in cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is an important cause of intracerebral hemorrhage. Its definite diagnosis still requires histopathologic demonstration of vascular amyloid. Thus, further improvement of noninvasive imaging methods would be desirable. Here we present 3 patients with histologically proved CAA, in which superficial cortical hemosiderosis and subarachnoid hemosiderosis were present in T2*-weighted MR images. Thus, we propose that these 2 findings might be valuable as noninvasive diagnostic markers for CAA.