The hereditary ataxias can be inherited in an autosomal dominant, autosomal recessive, or X-linked manner. Many types of autosomal dominant cerebellar ataxias for which specific genetic information is available are now known. Synonyms for autosomal-dominant cerebellar ataxias (ADCA) used prior to the current understanding of the molecular genetics were Maries ataxia, inherited olivopontocerebellar atrophy, cerebello-olivary atrophy, or the more generic term "spinocerebellar degeneration." (Spinocerebellar degeneration is a rare inherited neurological disorder of the central nervous system characterized by the slow degeneration of certain areas of the brain. There are three forms of spinocerebellar degeneration: Types 1, 2, 3. Symptoms begin during adulthood.) There are five typical autosomal-recessive disorders in which ataxia is a prominent feature: Friedreich ataxia, ataxia-telangiectasia, ataxia with vitamin E deficiency, ataxia with oculomotor apraxia (AOA), spastic ataxia. Disorder subdivisions: Friedreichs ataxia, Spinocerebellar ataxia, Ataxia telangiectasia, Vasomotor ataxia, Vestibulocerebellar, Ataxiadynamia, Ataxiophemia, and Olivopontocerebellar atrophy. There have been reported cases where a polyglutamine expansion may lengthen when passed down, which often can result in an earlier age-of-onset and a more severe disease phenotype for individuals who inherit the disease allele. This falls under the category of genetic anticipation. Several types of SCA are characterized by repeat expansion of the trinucleotide sequence CAG in DNA that encodes a polyglutamine repeat tract in protein. The expansion of CAG repeats over successive generations appears to be due to slipped strand mispairing during DNA replication or DNA repair.
PET-CT may also be beneficial in detecting extramedullary tumours in individuals diagnosed with SPB. CT imaging may be better than plain film radiography for assessing bone damage.An important distinction to be made is that a true plasmacytoma is present and not a systemic plasma cell disorder, such as multiple myeloma. The difference between plasmacytoma and multiple myeloma is that plasmacytoma lacks increased blood calcium, decreased kidney function, too few red blood cells in the bloodstream, and multiple bone lesions (collectively termed CRAB). Classification
Plasmacytoma is a tumor of plasma cells. The cells are identical to those seen in multiple myeloma, but they form discrete masses of cells in the skeleton (solitary plasmacytoma of bone; SPB) or in soft tissues (extramedullary plasmacytoma; EP). They do not present with systemic disease, which would classify them as another systemic plasma cell disorder.The International Myeloma Working Group (IMWG) has published criteria for the diagnosis of plasmacytomas. They recognise three distinct entities: SPB, extramedullary plasmacytoma and multiple solitary plasmacytomas (+/- recurrent). The proposed criteria for SPB is the presence of a single bone lesion, normal bone marrow (less than 5% plasma cells), small or no paraprotein, no related organ involvement/damage and a normal  skeletal survey (other than the single bone lesion). The criteria for extramedullary plasmacytoma are the same but the tumor is located in soft tissue. No bone lesions should be present. Criteria for multiple solitary plasmacytomas (+/- recurrent) are the same except either multiple solitary bone or soft tissue lesions must be present.