SAT-727 The Misdiagnosis Maze: Recognizing Double Sclerotic Bone Disease in the Shadow of Spondyloarthropathy

Abstract Disclosure: P. Porchezhian: None. P. Verma: None. K. Khanna: None. R. shukla: None. N. Midha: None. G. Bohra: None. Skeletal fluorosis, an endemic public health issue, is not clinically obvious until later stages and presents initially with aches, and fatigue when it is confused with rheumatological conditions. Undiagnosed cases progress to develop crippling deformities and neurological sequelae. Here we present a case of skeletal fluorosis, initially misdiagnosed as spondylitis, that was brought to clinical attention due to another unrelated etiology, finally paving the route to diagnosis. A 39-year-old gentleman was diagnosed with unclassified spondyloarthropathy due to back ache and radiological features of spinal sclerosis since last few years. Despite treatment, he had progressing skeletal deformities. He suddenly presented with a generalized tonic-clonic seizure to emergency. Evaluation revealed low serum calcium necessitating an endocrine reference. History revealed tetanic episodes over last few years and cataract surgery done in right eye at his 30 years age. He had non-inflammatory backache, peripheral joint stiffness which progressively worsened over years leading to restricted movements with no previous fractures. He had no prior neck surgery, radiotherapy, or autoimmune disorders. Examination showed left eye cataract, positive Chvostek and Trousseau signs, kyphosis, with fixed flexion deformity of both knees. Biochemistry revealed normal renal function, and high serum phosphorus with inappropriately low intact parathormone confirming hypoparathyroidism. Skeletal survey showed dagger spine appearance with no feature to suggest sacroiliitis, spinal longitudinal ligament and interosseous membrane ossification. There was high bone mass (Spine Z-score +10.5) with a Trabecular Bone Score of 1.694. Detailed history revealed similar features in few other residents in his locality and examination showed features of dental fluorosis. Suspecting skeletal fluorosis, urine and drinking-water fluoride levels done came out to be 4.4ppm (normal < 1.5ppm) and 2.6ppm (normal <1 ppm) respectively. He was managed with oral calcium and activated vitamin-D which led to symptomatic improvement. Drinking-water processing techniques were advised to curtail exposure. Spondyloarthropathy can be due to etiologies like autoimmune diseases including ankylosing spondylitis, diffuse idiopathic skeletal hyperostosis, etcetera. Hypoparathyroidism, in longstanding cases, may rarely have spondyloarthropathy. Another close mimic to be considered in endemic regions is skeletal fluorosis. Hypoparathyroidism and skeletal fluorosis both lead to sclerotic bone disease with poor bone microarchitecture, affects dental and renal systems. In our patient, the co-occurrence of two such sclerotic bone diseases not only led to severe morbidity and functional status for the patient but also posed a challenge and delay in diagnosis and management. Presentation: Saturday, July 12, 2025