a 36-year - old woman complained of an insidious onset of generalized myoclonus that first became apparent at age 27 years .
she had no perinatal problems and her development was normal in childhood and juvenile periods .
adult - onset myoclonus had worsened progressively from right hand to four extremities , tremulous voice and gait disturbance developed after 3 years from disease onset , and she could not continue working as a nurse .
she had no history of febrile convulsions or seizure , infectious disease in the central nervous system , exposure to toxic materials , or intake of herbal drugs .
her younger brother aged 40 years old also had progressive generalized myoclonus , which was detected 6 years ago at age 34 years ( figure 1 ) .
the patient was alert and oriented , and her mini - mental state examination score was 30 .
she did not have gaze palsy , and her vision and hearing were normal ; however , her voice was tremulous and generalized positive myoclonus was observed at four extremities and body .
negative myoclonus , dystonia , tremor , and rigidity were not detected , and both motor and sensory functions were intact .
there was no evidence of cerebellar dysfunction , and she did not have an ataxic or parkinsonian gait , although she staggered slightly because of myoclonus .
examination of the eyes revealed cherry - red spots ( figure 2 ) , but her electroencephalogram was normal .
no white matter lesion or cerebellar atrophy was detected in an mri of her brain ( figure 3 ) .
neuraminidase , hexosaminidase a , and -galactosidase activities in the leukocytes and cultured fibroblasts in patient and younger brother were normal .
the cherry - red spot is a pale perifoveal ring that develops when large deposits of lipid , sphingolipid , or oligosaccharide material accumulate in the ganglionic cells at the macula.2 this is a characteristic finding in storage diseases , including the sialidoses , gm1 and gm2 gangliosidoses , neuronal ceroid lipofuscinosis , niemann - pick disease ( groups a through d ) , farber s lipogranulomatosis , and metachromatic leukodystrophy .
interestingly , niemann - pick disease , farber s lipogranulomatosis , and metachromatic leukodystrophy are not associated with myoclonus . moreover
, the patient in this report did not have typical findings of these 3 diseases such as the organomegaly , cognitive impairment , and gaze palsy seen in niemann - pick disease4 ; the hoarseness , arthritis , and subcutaneous nodules seen in farber s lipogranulomatosis ; or the abnormal brain mri findings in metachromatic leukodystrophy .
in ceroid lipofuscinosis , sialidosis , gm1 and gm2 gangliosidoses , myoclonus , and maculopathy ( e.g. a cherry - red spot ) may coexist .
although they are quite similar in appearance , the macular abnormality seen in patients with neuronal ceroid lipofuscinosis ( which has been described as  bulls - eye maculopathy  ) can be distinguished from the cherry - red spot by color and shape , as well as by the decreased visual acuity and visual - field restriction that are common in neuronal ceroid lipofuscinosis.5 moreover , adult - onset lipofuscinosis has an autosomal dominant inheritance , rather than the autosomal recessive pattern seen in this patient.6 gm1 gangliosidosis results from a deficiency of -galatosidase ; the adult form ( type 3 ) presents as a slowly progressive dementia with prominent parkinsonian features and extra - pyramidal dysfunction , particularly dystonia.7 gm2 gangliosidosis results from a deficiency of hexosaminidase a ; the late form ( with an onset during adolescence and young adulthood ) may be characterized by cognitive dysfunction , cerebellar dysfunction , upper and lower motor neuron involvement , and extrapyramidal dysfunction.8 because -galatosidase and hexosaminidase activity was normal in this patient , because she has a normal level of intelligence , and because no other prominent pyramidal or extrapyramidal dysfunction was detected , we might not diagnose this patient as gm1 and gm2 gangliosidoses .
sialidosis is an inherited , autosomal recessive disease associated with a neuraminidase deficiency.9 it has 2 major clinical manifestations : type i ( late , adult onset ) and type ii ( early , infantile onset ) .
type i sialidosis is typically found in patients aged 8 to 25 years and is characterized by cherry - red spot myoclonus , seizure , neuropathy , corneal clouding , and difficulty walking , but with normal vision and intelligence ( obrien , 1978 ) .
type ii sialidosis is characterized by dysmorphism , myoclonus , mental retardation , ocular cherry - red spots , and hepatosplenomegaly .
the patient in this report may present clinical evidence of type i sialidosis , but her laboratory findings do not support this diagnosis ; activities of the neuraminidase were normal .
a similar case of progressive myoclonic epilepsy has been reported.10 differences from the previous report which described a patient with progressive myoclonic epilepsy , cherry - red spots and negative enzyme deficiency were theses ; 1 ) the onset - age was older than the previous report ( 27 versus 13 years , adult versus juvenile - onset ) ; 2 ) the patient had a sibling with same disease , which indicated she had inherited disease , but the patient in previous report did not have familial history ; 3 ) the patient in our report did not have a history of seizure , and it is different from the patient with myoclonic epilepsy . although the cause of cherry - red spot myoclonus is not clear , to our knowledge , this is the first report of adult - onset familial cherry - red spot myoclonus caused by an unknown type of lysosomal storage disease in korea .
 we report a case of a 36-year - old woman with progressive generalized myoclonus that first became apparent 9 years ago . 
 her younger brother had similar problems . 
 examination of her eyes revealed cherry - red spots . 
 hexosaminidase a , -galactosidase and neuraminidase activity were normal . 
 although the laboratory findings were negative , cherry - red spots , progressive myoclonus and autosomal recessive inheritance pattern suggested that she had an unknown type of lysosomal storage disease . 
Case Report
Discussion