Diffuse idiopathic skeletal hyperostosis (DISH) was first described by Forestier [
28] in the early fifties and subsequently named after him. When it became clear that peripheral enthesopathies frequently accompanied spinal pathology, suggesting a systemic skeletal condition instead of an isolated spinal disease, the name was changed into diffuse idiopathic skeletal hyperostosis to better describe the wide range of abnormalities possible [
29]. DISH can be distinguished from other ankylosing diseases such as ankylosing spondylitis (Morbus Von Bechterew), because bony joints, especially the sacroiliac joints are by definition preserved in DISH [
4].
Ossification of the posterior longitudinal ligament (OPLL) is a disease probably strongly related to DISH and has been studied in depth especially in Japan where it is a common condition [
30]. Inamasu et al. [
31] suggest from their literature review of previously conducted research on OPLL that it is probably not a single-gene disease; that pathways by which osteogenic induction of spinal ligament cells might occur are as yet poorly understood and that bone synthesis marker concentrations have not differed significantly from control groups. It is currently unknown whether the results obtained from research on OPLL may be applicable to DISH as well [
30].
In the population excavated from the ‘Pandhof’ of the OLVK in the city of Maastricht, DISH was the most frequently encountered pathology. Seventeen individuals with an average age at death of 49.5 years were diagnosed with this condition on the basis of spinal ligament ossification or multiple peripheral enthesopathies. The percentage of adult individuals with DISH therefore, was 40.4%. This is an unusual high percentage of DISH in a relatively young population compared to results from radiological studies in the literature [
7,
11]. In the study by Rogers and Waldron [
32], DISH was found to be present in 11.5% (6 out of 52 excavated males), of the population buried in the church and chapels from The Royal Mint Medieval site in London while the prevalence of DISH in a nearby lay cemetery where the general population (likely to be peasants/farmers), was buried, was 0% (0 out of 99 males). They suggested this difference in prevalence (11.5 vs
. 0%) to be caused by a difference in occupation and access to food [
33]. In the present study the prevalence of DISH was almost fourfold that reported by Rogers and co-authors. Janssen and Maat [
34], found in their paleopathological study DISH to be present in 100% of the inspected clergymen (
N = 27, with a mean age of 56 years ranging from 43 to 75 years and living between 1070 and 1521 CE) excavated from the Saint Servaas Basilica also in the city of Maastricht. Since the present study group has in common with the clergymen from the Saint Servaas Basilica that the individuals were probably enjoying a high status (as can be concluded from the location of their burial within the confines of the church normally reserved for priests, monks and high-status citizens), and likely had plentiful supply of food, it is not unreasonable to suggest that the associated ‘monastic way of life’, a term coined by Rogers and Waldron [
32], may have predisposed to DISH [
33,
35]. From descriptions of the dietary habits of monks in the Middle Ages in the discussion section of the Rogers article, it can be argued that saturated (animal-) fats combined with small portions of vegetables and ample alcoholic beverages may have often been on the menu, not unlike the diet of a considerable part of modern Western society. The 17 individuals with DISH from the present study were buried in the interval 450–1795
CE. Therefore, it is hypothesised that the interred of the OLVK (and the Merovingian Church before that), may in general have had an abundant food supply during this time period. Although genetic factors may play an important role in the etiology of DISH, to our best knowledge, no historical evidence suggests a closer genetical relationship between monks than between the general population and monks, therefore, a genetical predisposition for monks to develop DISH cannot be demonstrated. From current research it can be learned that high body mass index and insulin-independent diabetes mellitus are risk factors for developing DISH further supporting, though certainly not proving, that the lifestyle of ancient clergymen (sedentary work; abundance of food), may have predisposed them to develop DISH [
36,
37].
Examination of the skeletal material with severe abnormalities suggests that DISH may have seriously affected the locomotor and probably also cardiopulmonary apparatus of individuals with this condition. For example, ankylosis of the thoracic cage forced the individual from grave 25 to ventilate by diaphragm contraction only and this would have led to restriction of pulmonary function and subsequent physical impairment. Furthermore, when the physiological range of motion of multiple bony joints from the axial and peripheral skeleton becomes limited due to surrounding soft tissue ossification, it is not unreasonable to suggest that affected individuals may have had clinical symptoms that are detectable by physical examination. The individual from grave 25 probably also suffered from restricted abduction and endorotation (estimated to be between 45–60 degrees for both maneuvers before ossified soft tissue impingement), in the left glenohumeral joint. Due to postmortem absence of the articular surface of the humeral head on the contralateral side, no right shoulder impingement could be estimated.