MedGen

The disposition to develop an allergic or pseudoallergic reaction, the reaction itself or its consequences. [from SNOMEDCT_US]

The photoparoxysmal response (PPR), also referred to as photosensitivity, is defined as the abnormal occurrence of cortical spikes or spike and wave discharges on electroencephalogram (EEG) in response to intermittent light stimulation (Doose and Waltz, 1993). Photosensitivity is a frequent finding in patients with idiopathic generalized epilepsy (see 600669), especially those with juvenile myoclonic epilepsy, suggesting a common epileptogenic pathway for both phenomena. The comorbidity of the 2 disorders suggests that presence of PPR may also increase the risk for epilepsy (Stephani et al., 2004; Tauer et al., 2005). Genetic Heterogeneity of Photoparoxysmal Response The PPR1 locus has been mapped to chromosome 6p21. See also PPR2 (609572), mapped to chromosome 13q31, and PPR3 (609573), mapped to chromosome 7q32. [from OMIM]

A tendency to fall or the inability to keep oneself from falling; imbalance. The retropulsion test is widely regarded as the gold standard to evaluate postural instability, Use of the retropulsion test includes a rapid balance perturbation in the backward direction, and the number of balance correcting steps (or total absence thereof) is used to rate the degree of postural instability. Healthy subjects correct such perturbations with either one or two large steps, or without taking any steps, hinging rapidly at the hips while swinging the arms forward as a counterweight. In patients with balance impairment, balance correcting steps are often too small, forcing patients to take more than two steps. Taking three or more steps is generally considered to be abnormal, and taking more than five steps is regarded as being clearly abnormal. Markedly affected patients continue to step backward without ever regaining their balance and must be caught by the examiner (this would be called true retropulsion). Even more severely affected patients fail to correct entirely, and fall backward like a pushed toy soldier, without taking any corrective steps. [from HPO]

A rare reflex epilepsy characterized by seizures and photoparoxysmal responses triggered by flashing or flickering lights, or patterns. Exact nature of the stimulus and seizure type are variable. The disorder mainly presents in childhood and adolescence and can either occur as an isolated condition, or be associated to other epilepsy syndromes. [from ORDO]