List co-morbidities that may occur together with "Stiff man Syndrome"
SMS (Stiff man Syndrome) is is a rare disorder of the central nervous system of probable autoimmune origin and as such is associated with other autoimmune diseases, such as Insulin Dependent Diabetes Mellitus . GAD-65 is a dominant auto-antigen that is found both in in stiff-man syndrome and insulin-dependent diabetes mellitus. TRAB -positive Graves' disease has been reported to occur together with SMS. 
In a subgroup of patients with the stiff-man syndrome, the condition is likely to have an autoimmune paraneoplastic origin. The detection of autoantibodies against the 128-kd antigen in patients with this syndrome should be considered an indication to search for an occult breast cancer.

HCV may be the etiologic virus of progressive encephalomyelitis with rigidity; a rare disorder similar to stiff-man syndrome although different because it is progressive and fatal.
It is possible that the reported case of association of progressive dementia with concomitant development of stiff-man syndrome in an elderly man represents an exaggerated form of such motor disturbances in dementia, and that clinical and electromyographic features of stiff-man syndrome may be present with increased incidence in patients with dementia.