Tuberculous Encephalitis with Aphemia Detected Only by 18F-Fluorodeoxyglucose-Positron Emission Tomography.

Sir,

Tuberculous meningitis is a common cause of chronic meningitis in India. However, pure tuberculous encephalitis (TbE) is rare and overshadowed by meningitis or mass lesions such as tuberculomas. A 17-year-old girl presented with aphemia. Examination revealed a right upper motor neuron facial palsy with effortful speech, articulatory groping and buccofacial apraxia, with preserved verbal comprehension, reading, and writing (Aphemia). Oropharyngeal movements were normal. Abdominal lymph node biopsy 8 months earlier had shown reactive lymphadenopathy. Six months earlier, she had developed right-sided hearing loss and right lower motor neuron 7th nerve palsy. Magnetic resonance imaging (MRI) brain showed a left medial occipital lobe lesion along with a ring-enhancing lesion in the right petrous apex [Figure 1]. Cerebrospinal fluid (CSF) examination was normal, and she improved with intermittent steroid therapy (prednisolone 45 mg/day). As she refused a biopsy, prednisolone was continued with a provisional diagnosis of sarcoidosis. Mantoux test, angiotensin converting enzyme levels, Brucella IgM and IgG and a bacterial and fungal CSF polymerase chain reaction (PCR) panel were negative. One week earlier, she had come with transient speech arrest resolving after 24 h. Both times, MRI brain with contrast showed no new changes. Electroencephalogram (EEG) showed severe left hemispheric slowing, and she was administered intravenous levetiracetam and sodium valproate for presumed epileptic aphasia. However, continuous EEG monitoring for 4 days showed only left hemispheric slowing without any epileptiform discharges. 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) showed FDG avid adenoid tissue, as well as small mediastinal, para aortic, and abdominal lymph nodes along with multiple avid splenic lesions. There was a lytic lesion in the right petrous apex as well as diffuse FDG uptake in the left operculum and anterior cingulate gyrus [Figure 2].

Figure 1

Top panel; magnetic resonance imaging at admission (a-c). T1 contrast axial, fluid-attenuated inversion recovery (top right). (d) Diffusion image at 6 months. (e-g) Magnetic resonance imaging at 9 months. (h) Diffusionweighted magnetic resonance imaging at 30 months showing normal cerebral hemispheres. Mild hydrocephalus is seen

Figure 2

Positron emission tomography-computed tomography images showing (a); fluorodeoxyglucose avid right adenoid tissue (b) left opercular hypermetabolism at presentation (c) positron emission tomography-computed tomography at 9 months shows suprasellar hypermetabolism extending along the left middle cerebral artery. (d) Positron emission tomography-computed tomography at 9 months showing persistent left opercular and new medial frontal bilateral hyper-metabolism. (e) Outside positron emission tomography-computed tomography showing right sacral avid lesion. (f) Positron emission tomography-computed tomography at 18 months showing gross left cerebral hemisphere hypometabolism. (g) Positron emission tomography-computed tomography at 30 months showing persistent left cerebral hemisphere hypometabolism. (h) Arrow shows scanty acid-fast bacilli in adenoid tissue biopsy specimen (Ziehl–Neelsen stain)

Bone marrow biopsy and flow cytometry were normal. Adenoid biopsy showed scanty acid-fast bacilli (AFB), but GeneXpert and tuberculosis (Tb) PCR on the tissue were negative. Immunostaining of the specimen for lymphoma was negative. She was started on antituberculous treatment (ATT) (RHZE) with Dexa 12 mg/day. A repeat CSF examination showed 48 cells with 100% lymphocytes and normal protein. Two months later, she presented in a stuporous state. At month 9, a new MRI was suggestive of optochiasmatic arachnoiditis with endarteritis and mesodiencephalic infarcts. Steroids were escalated, and they left elsewhere for evaluation.

There, a repeat PET-CT showed a metabolically active irregular enhancing area along the basal cisterns extending along the middle cerebral artery branches bilaterally with a new lytic lesion in the right sacral ala and splenic FDG avid lesions. The sacral lytic lesion was biopsied. This time, AFB smear and GeneExpert for Mycobacterium tuberculosis were positive. She was started on 5-drug ATT (RHEZ + moxifloxacin) with steroids and came back to us for follow-up. An MRI at 18 months of treatment showed decreased enhancement around the suprasellar cistern. PET-CT showed diffuse left hemispheric hypometabolism, but her splenic lesion remained FDG avid at 18 months. Repeated MRIs at 9 and 18 months showed no new lesions and the opercular area remained normal. She continued 5 drugs ATT for 24 months and finally discontinued it herself. She remains ambulant with persistent aphemia. At 30 months’ follow–up, a repeat PET-CT showed persistent left cerebral hemispheric hypometabolism. MRI brain was normal.

As the bacillary load is low in TbE, the CSF PCR is negative, and diagnosis can be elusive. Initial CT or MRI scans are normal in 35% of patients with TbE, although eventually tuberculomas, miliary nodules, cerebritis, abscesses, ventriculitis, or arachnoiditis are found.[12]

18F-FDG PET/CT is very useful in the diagnosis of central nervous system infections increased tissue uptake of 18F-FDG is attributed to increased cell density, overexpression of GLUT-1 and GLUT-3 transporter isotypes and by increased hexokinase activity. FDG PET in tuberculomas may show a characteristic ring-like or “doughnut” pattern, with low uptake within the abscess cavity and peripheral increased uptake.[34] 18F-FDG PET/CT findings usually correlate with MRI abnormalities.

In encephalitis, FDG PET shows hypermetabolism in the active stage and hypometabolism in the chronic stage.[5] In autoimmune encephalitis, such as N-methyl D-aspartate receptors encephalitis, a mixed picture of hyper- and hypo-metabolism is encountered.[6] Our patient also demonstrated serial evolution of FDG-PET changes from hypermetabolism to hypometabolism in the opercular region after the initiation of ATT.

In our patient, the serial evolution of PET-CT changes along with AFB positivity with biopsy from 2 disparate sites and suggested an inflammatory lesion, consistent with TbE [Table 1]. Our patient exhibited two unusual characteristics. 18F-FDG PET/CT showed a focal encephalitis in the left frontal opercular area with consistently normal MRI findings in this region. Moreover, her FDG PET findings evolved with time consistent with the resolution of her TbE. Second, she presented with an unusual case of aphemia secondary to the TbE.

Table 1

Compilation of magnetic resonance imaging and positron emission tomography-computed tomography findings over time

Time scale	MRI brain	FDG PET-CT
6 months before presentation	Left medial occipital lobe lesion and ring enhancing lesion in the right petrous apex	Not done
At admission	Left medial occipital lobe lesion and ring enhancing lesion in the right petrous apex.Normal opercular region	FDG avid adenoid tissue, and small mediastinal, para aortic and abdominal lymph nodes as well as multiple avid splenic lesions Lytic lesion in the right petrous apex as well as diffuse FDG uptake (hypermetabolic) in the left operculum and anterior cingulate gyrus
9 months	Features of optochiasmatic arachnoiditis with endarteritis and mesodiencephalic infarctsNormal opercular region	FDG avid metabolically active enhancing areas along the basal cisterns extending along the MCA branches bilaterally with a new lytic lesion in the right sacral ala and splenic FDG avid lesions
18 months	Decreased enhancement around the suprasellar cistern. Remote mesodiencephalic infarctsNormal opercular region	Diffuse left hemispheric hypometabolism with FDG avid splenic lesions
30 months	Normal scan except for mild brain atrophy	Persistent left cerebral hemispheric hypometabolism. Active splenic lesions

FDG=18F-fluorodeoxyglucose, MRI=Magnetic resonance imaging, PET-CT=Positron emission tomography-computed tomography, MCA=Middle cerebral artery

Aphemia (Cortical anarthria) lies in a continuum of articulatory and language disorders [Supplementary Figure 1]. It is often called an apraxia of speech. The lesion implicated lies in the left precentral gyrus near the face area in the frontal lobe.

In conclusion, 18F-FDG PET/CT may detect areas affected by TbE, even if the MRI is normal. 18F-FDG PET-CT is also useful in the assessment of treatment response to Tb as a reduction in hypermetabolism often precedes radiological improvement.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

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Conflicts of interest

There are no conflicts of interest.

Flow chart demonstrating various articulatory disorders. Buccofacial apraxia has been included in view of its frequent association with these conditions