AxD were divided into three forms traditionally based on the age of onset: infantile, juvenile and adult. Early onset AxD was prominently frontal-lobe involved and characterized by bilateral white-matter lesions. The clinical and neuroradiological
presentation of adult onset AxD is very different from that of early onset AxD. The
abnormalities of adult onset AxD are mainly concentrated in the brainstem-spinal cord junction and typically experience pseudobulbar symptoms such as dysarthria and
dysphonia, ataxia and palatal myoclonus. While the neurological characteristics of
adult onset AxD are well documented as above mentioned, there is sparse information
about neuropsychiatric symptoms. The MRI features of our patient is more consistent
with leukodystrophy. The clinical presentation and neurological findings of leukodystrophy are often nonspecific. Psychiatric manifestations especially psychoses
have been commonly described in leukodystrophies; however, association of
psychoses with AxD has been rarely reported. Occasionally a case of adult onset AxD
that was concurrent with cerebral contusion presenting with demented symptoms was
reported [2]. Occasional case reports of mild cognitive, visual, and auditory abnormalities in adult onset AxD are on record. Psychogenic polydipsia is
characterized by excessive fluid intake and accompanied by compensatory polyuria.
Psychogenic polydipsia is caused by psychiatric disorders, often schizophrenia
spectrum disorder, with an incidence of 11 to 20%. The onset of polydipsia and psychiatric symptoms was very insidious in our patient. Thus, faced with a patient
with progressive mental disorder and leukodystrophy on MRI, a genetic investigation
of GFAP gene is recommended.
In adult onset AxD, an extensive white matter involvement on MRI in our patient is as rare as her psychiatric manifestations. MRI plays an important role in diagnosis of adult onset AxD because of a wide range of clinical presentation in this group. Detailed neuroradiologic findings included medulla oblongata and cervical spinal cord atrophy, hilum of dentate nucleus hyperintense and periventricular white matter abnormalities. Although the characterizations of MRI in the adult-onset group displayed diversified signs, many do show a unique tadpole-like feature of brain stem and upper cervical cord, which is characterized by marked atrophy of the medulla oblongata and cervical spinal cord, although the pontine base remains intact [3, 4]. The leukodystrophy in MRI is not prominent in adult variants. Approximately 90% cases showed marked medulla oblongata atrophy and 50% had deep or periventricular white matter lesions [1]. Supratentorial periventricular abnormalities and cerebral involvement are less likely to appear in patients with age over 40 years at onset of the disease [5]. In our case, MRI findings showed severe hyperintensity of extensive periventricular white matter without atrophy in medulla oblongata and cervical spinal cord which is rare in adult onset AxD.
Our report enriches the understanding of familial adult onset AxD. To the best of our knowledge, this is perhaps the first case report of adult onset AxD presenting as psychogenic polydipsia in the world literature. This study expands the mutation spectrum of leukodystrophy presenting with psychiatric manifestations.