Colloid (hyaline) inclusion bodies in the central nervous system: their presence in the substantia nigra is diagnostic of Parkinson's disease.

Intracytoplasmic "colloid" inclusions have been described within neurons of several discrete central nervous system nuclei in a variety of entities. Although they lack specificity for any particular disease, they are believed to represent one of the morphologic changes of neuronal aging. Because premature aging of the substantia nigra has been one of the claimed mechanisms occurring in Parkinson's disease, the prevalence of colloid inclusions was studied within the substantia nigra in 15 patients with Parkinson's disease, 15 age-matched controls, 50 "normal" individuals, 10 patients with dementia of Alzheimer's type, and two patients with amyotrophic lateral sclerosis. Colloid bodies were found in the substantia nigra of all patients with Parkinson's disease and were virtually absent in the other populations. Histochemical and ultrastructural analyses showed that colloid bodies differ from early and mature Lewy bodies. They may represent the "pale" inclusions rarely mentioned in the literature and often mistaken for early Lewy bodies. "Colloid" bodies in the substantia nigra are diagnostic of Parkinson's disease. These findings support the theory of "premature" aging of the substantia nigra in this disease.