When seizures are not seizures: pseudohypoparathyroidism with symptomatic hypocalcemia mimicking epileptic events in a patient with lesional neocortical temporal lobe epilepsy

Abstract

Case Presentation: A 23-year-old right-handed man with left posterior temporal lobe lesional focal epilepsy due to ipsilateral frustrated hemimegalencephaly was admitted to the emergency department for new-onset paroxysmal tonic episodes of the upper limbs that began on the same day, each lasting several minutes with spontaneous cessation. During the preceding week, the patient reported progressive blurred vision and oscillatory vertigo that had not improved with empirical corticosteroid therapy. Discussion: Initially, seizure recurrence was suspected, as the patient’s typical aura involved dizziness. However, the semiology was different: while his previous seizures were focal impaired-awareness seizures evolving to bilateral tonic–clonic seizures, the current episodes featured preserved consciousness without secondary generalization. Involvement of the supplementary motor area (SMA) was considered unlikely due to the absence of speech or motor planning deficits. Furthermore, the patient had been seizure-free for five years on a stable medication regimen. Psychogenic non-epileptic events were also considered, although the sustained tonic contractions appeared atypical for a functional movement disorder. Additional metabolic evaluation showed severe hypocalcemia, marked hyperphosphatemia, markedly elevated parathyroid hormone levels (>1366 pg/mL), mild hypokalemia, and vitamin D deficiency. Serum magnesium, renal function, and vitamin B12 levels were normal, and there was no evidence of malabsorption. Skeletal imaging revealed metabolic bone changes, including trabecular abnormalities with lytic areas on cranial, pelvic, and femoral radiographs. Bone densitometry showed low bone mass for age at the distal radius, and bone scintigraphy demonstrated increased osteoblastic activity in the skull, sternum, right ninth rib, and right tibia. The patient did not exhibit phenotypic features of Albright hereditary osteodystrophy, such as short stature, rounded facies, or brachydactyly, and genetic testing for GNAS mutation was negative. Final Comments: A diagnosis of symptomatic severe hypocalcemia secondary to pseudohypoparathyroidism type 1b was made. Treatment with calcium and vitamin D replacement resulted in complete resolution of the paroxysmal motor symptoms, with no further events after correction of serum calcium levels. This case highlights an important diagnostic pitfall in epileptology: not all paroxysmal motor events in patients with epilepsy represent seizure recurrence. Severe hypocalcemia may produce tetanic episodes that closely resemble epileptic seizures. Careful analysis of semiological differences from habitual seizures are essential to avoid misdiagnosis, unnecessary escalation of antiseizure therapy, and delayed treatment of reversible metabolic disorders.