Unusual cause of progressively impaired cognitive function: <i>Mycobacterium avium</i> complex meningoencephalitis

Mycobacterium avium complex (MAC) is a rare cause of meningoencephalitis. Non-tuberculous mycobacterium meningoencephalitis including MAC meningoencephalitis is an important cause of rapidly progressive dementia. We present a case of MAC meningoencephalitis in an immunosuppressed woman who had progressively impaired cognitive function. An 83-year-old woman who had been taking glucocorticoid for myasthenia gravis developed cognitive dysfunction and visual hallucinations over a period of 2 weeks. Cerebrospinal fluid (CSF) findings were normal, but MAC was positive in CSF culture and M. avium and M. intracellulare were identified by PCR. She was treated with multiple antimycobacterial agents and her symptoms fully recovered. MAC meningoencephalitis is an unusual cause of progressively impaired cognitive function. The possibility of mycobacterial central nervous system infection cannot be excluded by normal CSF findings.