Stellate Multiform Amelanotic Choroidopathy (SMACH)
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Disease
Stellate multiform amelanotic choroidopathy (SMACH) is a recently described choroidal pathology with unique multimodal imaging features.[1] Clinically, it is characterized by a multiform lesion, frequently associated with serous retinal detachment (in around 59%) noted on optical coherence tomography (OCT) and overlying retinal pigment epithelial (RPE) changes.[1] It was first reported by van Dijk and Boon in 2021 under the designation of “serous maculopathy due to aspecific choroidopathy” (SMACH).[2] Since then, at least 17 additional cases with similar imaging patterns have been reported in the literature.[1] [3] As subretinal fluid was not present in some of these cases, Ramtohul et al. proposed a nomenclature change to “stellate multiform amelanotic choroidopathy”, to maintain its former abbreviation, SMACH.[1]
Etiology
The etiology of SMACH is unknown. A choroidal origin has been proposed, with early onset of disease and lesion size stability pointing to a congenital dysgenesis.[1] An atypical staphyloma found in some of the affected individuals suggests that choroidal flow turbulence could also play a role.[3]
Risk Factors
A retrospective review including 18 patients diagnosed with SMACH found that the majority were young individuals (mean age 28 ± 19 years), with a similar gender distribution (10 men and 8 women).[1]
General Pathology
The lack of pathological data limits the current understanding of the etiology and pathophysiology of SMACH.[1]
Pathophysiology
It is theorized that subretinal fluid accumulation in SMACH results from choriocapillaris compression by the choroidal lesion, increasing hydrostatic pressure, and damage to the outer blood-retinal barrier.[1][2]
Diagnosis
SMACH is a clinical diagnosis suspected after fundoscopy and confirmed by characteristic findings in multimodal imaging evaluation, comprising near-infrared reflectance (NIR), optical coherence tomography (OCT), fundus autofluorescence (FAF), fluorescein and indocyanine green angiography (FA, ICGA) and OCT angiography.[1][2][3] A large study on SMACH included 'eyes with findings on multimodal imaging consistent with SMACH, defined as serous retinal detachment associated with pigmentary changes on ophthalmoscopy, disruption and elevation of the RPE by a thickened and structurally altered choroid on OCT, hypofluorescent and hyperfluorescent changes on FA (fluorescein angiogram), absence of focal choroidal hyperpermeability on indocyanine green angiography (ICGA), and absence of macular neovascularization (MNV) on OCT angiography (OCTA). Extramacular lesions or eyes without serous retinal detachment but showing a similar imaging pattern were also included.'[2][1]
Symptoms
Affected individuals can be asymptomatic or complain of gradual vision loss or metamorphopsia.[1]
Signs
On ophthalmoscopic examination, SMACH appears as a unilateral, yellowish-orange, dendriform lesion. Radial, finger-like protrusions extending from the lesion in a stellate configuration are the distinguishing features of this diagnosis. Fine hypo/hyperpigmentation can be seen, corresponding to retinal pigment epithelium (RPE) changes. Most reported cases are located in the macula, but extrafoveal forms have also been described.[1][2] The images of a representative case can be accessed here.[3] The stellate pattern or dendritic protrusions from the lesion are better visible with en-face structural OCT, near-infrared reflectance, and early stage ICGA.[1] Enface OCT usually reveals more finger-like projections compared to ophthalmoscopy.
Diagnostic procedures
Reported SMACH features on multimodal imaging include:[1][2][3]
- NIR: A hyperreflective lesion layout is reproduced, highlighting the radial projections making up its stellate shape.
- OCT: Cross-sectional OCT shows choroidal architecture disorganization with irregular hyperreflective thickening of the inner choroid ('hyperreflective fibrous-like changes').[1] Subretinal fluid, RPE elevation (anterior protrusion of RPE) and outer retinal disruption may be seen above the lesion, while choroidal stromal hyperreflectivity may be noted below. Normal outer choroidal (Haller) vessels and choroidoscleral junction may be noted.
- FAF: Both normal, speckled hypoautofluorescence (from RPE alteration) and annular hyperautofluorescence (due to vitelliform lesion) patterns have been described.
- FA: Granular hypo/hyperfluorescence (from RPE changes).
- ICGA: Early and late hypofluorescent lesion layout, with characteristic finger-like projections. Choroidal vascular permeability is not seen.
- OCTA: En-face OCTA segmented at the level of the inner choroid reveals a hyperreflective lesion with the aforementioned morphology.
Differential diagnosis
SMACH may masquerade early onset chorioretinal pathology, namely
- central serous chorioretinopathy,
- Best vitelliform macular dystrophy,
- placoid chorioretinitis and
- choroidal tumors [amelanotic choroidal nevus or melanoma, choroidal osteoma, choroidal metastasis, choroidal lymphoma, choroidal hemangioma, and focal scleral nodule (previously called solitary idiopathic choroiditis).[1][4]
Management
There is no consensus on the management of SMACH due to its novel description and few cases reported in the literature. Nonetheless, there was no improvement with photodynamic therapy or intravitreal anti-VEGF injections in the retrospective review published.[1] The associated subretinal fluid may fluctuate spontaneously.
Prognosis
The natural course of SMACH is punctuated by spontaneous fluctuation of the subretinal fluid, while the size of the choroidal lesion remained stationary (non-progressive nature). Vision loss may be related to subretinal fluid accumulation and/or outer retinal disruption. During the follow-up period of the retrospective review (mean duration 9 years), best corrected visual acuity remained relatively stable.[1]
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 Ramtohul P, Pellegrini M, Pichi F, et al. STELLATE MULTIFORM AMELANOTIC CHOROIDOPATHY: Clinical and Multimodal Imaging Features. Retina. 2023;43(9):1448-1461. doi:10.1097/IAE.0000000000003826
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 van Dijk EHC, Boon CJF. Serous business: Delineating the broad spectrum of diseases with subretinal fluid in the macula. Prog Retin Eye Res. 2021;84:100955. doi:10.1016/j.preteyeres.2021.100955
- ↑ 3.0 3.1 3.2 3.3 3.4 van Dijk EHC, Ossewaarde-van Norel J, Vingerling JR, Cohen SY, Boon CJF. Serous Maculopathy Due to Aspecific Choroidopathy (SMACH). Asia Pac J Ophthalmol (Phila). 2023;12(5):496-498. doi:10.1097/APO.0000000000000550
- ↑ Fung AT, Waldstein SM, Gal-Or O, et al. Focal Scleral Nodule: A New Name for Solitary Idiopathic Choroiditis and Unifocal Helioid Choroiditis. Ophthalmology. 2020;127(11):1567-1577. doi:10.1016/j.ophtha.2020.04.018
