Beyond the triad: akinetic mutism in idiopathic normal pressure hydrocephalus, with response to shunt placement. Illustrative case

Abstract

Background: Idiopathic normal pressure hydrocephalus (iNPH) typically manifests with the classic Hakim-Adams triad of gait disturbance, cognitive impairment, and urinary incontinence. While akinetic mutism represents a rare and severe neurological presentation characterized by profound reduction in voluntary movement and speech, its association with iNPH remains underrecognized in clinical practice. This case illustrates both the diagnostic challenges and remarkable therapeutic potential when encountering this unusual manifestation of iNPH.

Observations: A previously healthy 52-year-old female developed progressive gait instability, urinary incontinence, and cognitive decline over 6 months, followed by 3 months of akinetic mutism. Examination demonstrated characteristic features of iNPH including paratonic rigidity, magnetic gait, and frontal release signs. Neuroimaging revealed moderate ventriculomegaly with an Evans index of 0.38 and hyperdynamic CSF flow dynamics (peak velocity 7.4 cm/sec, stroke volume 95 µL). The patient exhibited dramatic clinical improvement within 1 week of ventriculoperitoneal shunt placement, with complete resolution of akinetic mutism and significant recovery of other symptoms sustained at the 6-month follow-up.

Lessons: This case underscores that akinetic mutism, while uncommon, may represent a severe but treatable manifestation of iNPH. The rapid reversal of akinetic mutism following CSF diversion highlights the importance of considering iNPH even in atypical presentations. Quantitative CSF flow analysis emerges as a valuable diagnostic tool in such challenging cases, while the striking clinical response reinforces the potential for complete functional recovery with timely intervention. https://thejns.org/doi/10.3171/CASE25257.

Keywords: akinetic mutism; cerebrospinal fluid dynamics; hydrocephalus biomarkers; idiopathic normal pressure hydrocephalus; reversible dementia; ventriculoperitoneal shunt.

FIG. 1.

Preoperative MRI findings in iNPH with akinetic mutism. A: Axial T2-weighted MR image demonstrating moderate bilateral supratentorial ventriculomegaly (Evans index 0.38; normal < 0.3), with blunting of the frontal horns and rounding of the third ventricular recesses, consistent with communicating hydrocephalus. B: Sagittal T2-weighted MR image confirming patency of the cerebral aqueduct (arrow) without obstruction, ruling out aqueductal stenosis. C: Axial FLAIR sequence revealing diffuse sulcal prominence (asterisks) and scattered periventricular/subcortical white matter hyperintensities (dotted arrow), indicative of chronic small-vessel ischemic changes. The absence of transependymal CSF seepage argues against acute hydrocephalus. These findings collectively support a diagnosis of iNPH with secondary microvascular injury.

FIG. 2.

Quantitative CSF flowmetry at the cerebral aqueduct. Phase-contrast MRI during peak systole shows hyperdynamic CSF flow dynamics as demonstrated in the velocity-time curve (A), which shows CSF in both diastole (above the baseline) and systole (below the baseline): peak velocity (7.4 cm/sec; normal range 2–5 cm/sec) and stroke volume (95 µL; pathological threshold > 42 µL), measured at the level of the cerebral aqueduct (circles) in axial T2-weighted (B) and phase (C) images, respectively. Phase shifts across the aqueduct are converted to velocity values (in cm/sec), and velocities are averaged across the aqueductal area to reduce noise. The exaggerated flow pulsatility reflects impaired ventricular compliance and altered CSF redistribution, characteristic of iNPH. These hydrodynamic abnormalities likely contribute to periventricular shear stress and dysfunction of adjacent mesencephalic arousal pathways, potentially exacerbating akinetic mutism.

FIG. 3.

Postoperative shunt placement and immediate anatomical outcome. Postoperative day 1 noncontrast axial CT scans confirming optimal placement of the ventriculoperitoneal shunt catheter via the right Keen’s point. The catheter tip is positioned in the occipital horn of the right lateral ventricle, with no immediate complications (e.g., hemorrhage or malposition). Early reduction in ventricular size is not expected at this stage; follow-up imaging at 6 months (not shown) demonstrated sustained decompression correlating with clinical improvement.