Stellate Multiform Amelanotic Choroidopathy (SMACH) is a rare choroidal disease first reported by van Dijk & Boon in 2021.
The initial case series comprised 18 patients (28 eyes), with a mean age of onset of 28 years (range: 10–58 years), relatively young. No clear data on sex differences are currently available. The disease name derives from the morphological characteristics of the lesions: stellate, multiform, and amelanotic.
The term “amelanotic” indicates that the lesions appear yellow-orange without melanin pigment. Which layer of the choroid the lesions occur in has not been pathologically confirmed at this time.
QHow rare is SMACH?
A
At the time of the initial report (2021), only 18 cases had been reported, and the number of cases worldwide is extremely small. The naming and establishment of the disease concept are recent, and there may be overlooked cases.
On fundus examination, a yellow-orange choroidal lesion is observed. The morphology is stellate or dendritic, with multiple finger-like projections. This characteristic appearance is the basis for the name SMACH. Lesions may be solitary or multiple, and both unilateral and bilateral cases have been reported.
In cases with subretinal fluid (SRD), serous retinal detachment may occur in the macula.
Findings from multimodal imaging are shown below.
Structural Imaging
NIR (Near-infrared reflectance): The stellate or dendritic pattern of the choroidal lesion is clearly visualized as hyperreflectivity. It is one of the most useful modalities for assessing the extent of the lesion.
OCT (Optical coherence tomography): Irregularities of the retinal pigment epithelium (RPE) over the choroidal lesion and the presence or absence of subretinal fluid can be confirmed. It is also used to evaluate choroidal thickness.
Fundus autofluorescence (FAF): Changes in autofluorescence are observed in the lesion area, indirectly reflecting RPE function.
ICGA (Indocyanine green angiography): Excellent for evaluating choroidal circulation, allowing detailed assessment of the intrachoroidal localization of the lesion. Both hyperfluorescent and hypofluorescent patterns have been reported.
Blood flow evaluation
OCTA (Optical Coherence Tomography Angiography): Non-invasively evaluates blood flow in the choriocapillaris (CC) of the lesion. In some cases, areas of reduced CC blood flow correspond to the stellate lesion.
QWhat is the most important test for diagnosing SMACH?
A
No single test confirms the diagnosis; multimodal imaging combining NIR, OCT, FA, and ICGA is the basis for diagnosis. In particular, NIR makes it easy to visually identify the stellate pattern of the lesion. For details, see the “Diagnosis and Testing Methods” section.
Only 17–18 cases have been reported, and no systematic epidemiological studies have been conducted. No clear risk factors have been identified.
As a possible mechanism, congenital choroidal dysplasia has been proposed. This is based on the frequent onset in young individuals and the similarity of lesion morphology to developmental abnormalities. However, histopathological data are currently unavailable.
The diagnosis of SMACH is based on a combination of characteristic fundus findings and multimodal imaging findings. There are currently no unified international diagnostic criteria for a definitive diagnosis.
Best disease involves the fovea and is diagnosed by EOG
Choroidal tumor
Yellow-orange elevated lesion
Tumor is more elevated and irregular
Differentiation from CSC is clinically important. CSC is part of the pachychoroid disease spectrum and is associated with choroidal vascular dilation 2). The stellate dendritic pattern of SMACH is not seen in CSC, and differences in findings on ICGA and OCTA are useful for differentiation.
There is no established standard treatment for SMACH. All reported treatment attempts to date are based on a limited number of cases.
Photodynamic therapy (PDT): Attempted in some cases, but no clear efficacy has been demonstrated.
Anti-VEGF therapy: Used in cases with subretinal fluid, but evidence of efficacy is similarly insufficient.
Observation: In many cases, the lesion follows a chronic stable course, so observation is the mainstay of management.
QWill vision worsen without treatment?
A
In many cases, the lesion follows a chronic stable course. However, if subretinal fluid extends to the macula, it may affect vision. Regular follow-up is important to detect changes early.
Stellate choroidal lesions are thought to compress the choriocapillaris (CC) from the outside, increasing hydrostatic pressure within the CC. This rise in hydrostatic pressure promotes fluid leakage through Bruch’s membrane and the RPE, leading to subretinal fluid accumulation.
Association with choroidal venous outflow obstruction
Choroidal venous outflow obstruction may be involved in the pathogenesis of SMACH. Cheung et al. argued that in the pachychoroid disease spectrum, dilation of large choroidal veins, including Haller’s veins, reflects choroidal venous outflow obstruction 2). A similar mechanism may be at work in SMACH, causing local choroidal circulatory insufficiency at the site of stellate lesions.
Stage 1: Lesion formation
Congenital malformation: A congenital abnormality in the morphology and structure of the choroid may be the underlying basis.
Development of stellate lesions: Yellow-orange non-pigmented lesions form within the choroid.
Stage 2: Compression and occlusion
CC compression: Stellate lesions compress the choriocapillaris, reducing local blood flow.
Venous outflow obstruction: Choroidal venous circulation is impaired, leading to increased hydrostatic pressure 2).
Stage 3: Fluid accumulation
RPE dysfunction: Increased hydrostatic pressure impairs the RPE pump function.
SRD formation: Fluid accumulates in the subretinal space through Bruch’s membrane and the RPE, resulting in serous retinal detachment.
Since its first report in 2021, SMACH is an extremely rare disease with only 17 to 18 reported cases. The establishment and naming of the disease concept itself is recent, and there may be a certain number of overlooked cases due to low awareness.
Changes in Naming and Organization of Disease Concept
Since the initial report (van Dijk & Boon, 2021), discussions on the disease name and concept have continued, and there is still no established international unified name. Descriptions such as “non-pigmented choroidopathy” and “stellate choroidopathy” are also seen in the literature.
Lack of pathological data: The histological characteristics of the lesions are currently unknown, and pathological studies are needed.
Unclear long-term prognosis: Due to the small number of cases, the long-term visual prognosis and full extent of lesion progression remain unknown.
Search for effective treatments: The efficacy of PDT and anti-VEGF is currently limited, and new therapeutic approaches need to be explored.
Need for epidemiological studies: Multicenter collaborative studies are essential to estimate risk factors, genetic background, and prevalence.
QHow will SMACH research proceed in the future?
A
Currently, the number of cases is small, and research at a single institution has limitations. The establishment of an international case registry and multicenter collaborative studies will be the next steps toward elucidating the natural history, pathology, and treatment of the disease.
