Keywords
I-123 MIBG - autonomic neuropathy - Ogilvie's syndrome - pseudo-obstruction - sympathetic
dysfunction
Case Report
A 48-year-female presented with a complex history of chronic back pain with frequent
episodes of hospitalization due to pseudo-obstruction with history of dysautonomia
for the last 2 years. The contrast-enhanced computerized tomography (CECT) scan in
the axial ([Fig. 1A]), coronal ([Fig. 1B]), and sagittal plane ([Fig. 1C]) showed nonspecific large bowel dilatation proximal to the short segment narrowing
in the distal sigmoid colon, with no feature of true obstruction. Colonic transit
capsule study was normal with no transit delay. The patient progressively had swallowing
difficulty, which on video fluoroscopy study was diagnosed with pharyngeal and esophageal
phase dysphasia. She later developed unexplained spastic paraplegia with sustained
clonus and autonomic pain over time period. The patient had a family history with
mother having similar neurological disorder, hence genomic testing was considered.
The hereditary spastic paraparesis genomic test for 129 gene and autoimmune autonomic
ganglionopathy was negative. The plasma concentration of norepinephrine was within
normal limits. Patient was suspected with poorly characterized syndrome of autonomic
failure and considered for cardiac 123-iodine metaiodobenzylguanidine (I-123 MIBG)
scan for the assessment of the autonomic dysfunction. The cardiac I-123 MIBG scan
showed reduced myocardial uptake in the early (15minutes) ([Fig. 2A]) and delayed (4hours) ([Fig. 2B]) images, with the quantification of heart and mediastinal (H/M) ratio at early time
point of 15minutes 1.58 (control: 2.81)[1] and at delayed time point of 4hours 1.54 (control: 3.04).[1] The findings were suggestive of cardiac sympathetic denervation. The findings supported
the diagnosis of progressive autoimmune autonomic neuropathy and hereditary spastic
paraparesis with gastrointestinal and cardiac dysfunction. The patient was symptomatically
treated, with nasojejunal feeding and cold octreotide therapy.
Fig. 1 Contrast-enhanced computed tomography (CECT) scan in the (A) axial, (B) coronal, and (C) sagittal planes shows narrowing in the distal sigmoid colon with nonspecific proximal
large bowel dilatation.
Fig. 2 The cardiac 123I MIBG scan with the quantification of heart and mediastinal (H/M) ratio at the early
time point of 15 minutes and at the delayed time point of 4 hours showed a reduced
(H/M) ratio (A) at the early time point of 1.58 (control: 2.81) and (B) at the delayed time point 1.54 (control: 3.04).
Discussion
Ogilvie's syndrome, or acute colonic pseudo-obstruction (ACPO), is a rare multifactorial
disorder that consists of dilatation of part or all of the colon and rectum. The pathophysiology
of ACPO is incompletely understood with an imbalance of sympathetic and parasympathetic
innervations, being the most widely-postulated theory. However, recently sacral parasympathetic
denervation causing atonic distal colonic segment similar to adynamic ileus is suspected
as the likely postulated cause.[2]
[3]
The parasympathetic nerve endings release acetylcholine, activating the muscarinic
receptors stimulating the plexus activity of entire nervous system, leading to stimulation
of bowel movements, gastrointestinal secretion, and blood flow. However, the sympathetic
nerve endings release norepinephrine, which inhibits both the plexus of the enteric
nervous system through activation of the α1, α2, and β adrenergic receptors. The effects of sympathetic nervous system are further
augmented by a presynaptic norepinephrine-mediated inhibition of release of parasympathetic
acetylcholine.[4]
I-123 MIBG as a radionuclide tracer is an analogue of norepinephrine, and concentrated
in adrenergic neurons in the presynaptic vesicles, the concentration reflects scintigraphic
display of the adrenergic nervous system. The change in concentration of myocardial
sympathetic innervation reflects neuronal integrity and functions.[5]
[6] The autonomic nervous system abnormalities may be regional, with the adrenergic
nerves of the heart particularly vulnerable to the effect of this disease.[6] The scintigraphic display of the adrenergic nervous system with the late H/M ratio
is an index of relative distribution of sympathetic nerve terminal offering information
about neuronal integrity and function.[7] I-123 MIBG has been reported to provide information regarding cardiac sympathetic
function in heart disease, Parkinson's disease, myotonic dystrophy, multiple system
atrophy, diabetes mellitus, and Chagas heart disease.[5]
[8]
[9]
[10]
Conclusion
This case demonstrates the potential use of I-123 MIBG scintigraphy for the assessment
of the autonomic function of sympathetic denervation with correlation with MIBG uptake
in clinical condition as progressive degenerative autoimmune autonomic neuropathy.
