Tracking down the White Plague: The skeletal evidence of tuberculous meningitis in the Robert J. Terry Anatomical Skeletal Collection

Paleopathological diagnosis of tuberculosis (TB) essentially relies on the identification of macroscopic lesions in the skeleton that can be related to different manifestations of TB. Among these alterations, granular impressions (GIs) on the inner skull surface have been considered as pathognomonic features of tuberculous meningitis (TBM). GIs may be established by pressure atrophy of the tubercles formed on the outermost meningeal layer during later stages of TBM. Although GIs were used as diagnostic criteria for TBM in the paleopathological practice since the late 20(th) century, their diagnostic value has been questioned. To contribute to strengthening the diagnostic value of GIs, a macroscopic investigation–focusing on the macromorphological characteristics and frequency of GIs–was performed on skeletons of known cause of death from the Terry Collection. The χ(2) analysis of our data revealed that GIs were significantly more common in individuals who died of TB than in individuals who died of non-TB causes. Furthermore, GIs were localized on the inner surface of the skull base and of the lower lateral skull vault. The localization pattern and distribution of GIs on the endocranial surface resemble that of the tubercles observed in the affected meninges during the pathogenesis of TBM. Our results strengthen the tuberculous origin of GIs and imply that they can be considered as specific signs of TBM. Therefore, GIs can be used as diagnostic criteria for TBM in the paleopathological practice, and the diagnosis of TBM can be established with a high certainty when GIs are present in ancient human bone remains.