PMC9704848_01
Initial findings in the patient. (a) Photograph taken before biopsy surgery shows acne on the face, being especially prominent over the lateral aspect of the left eyebrow. The black dots are the markings for surgery. (b) CT shows the osteolytic lesion on the left frontal bone. (c) T1-weighted gadolinium-enhanced MRI demonstrates marked contrast enhancement at the site of osteolysis. Contrast enhancement is also evident in the surrounding dura, temporalis muscle and subcutaneous tissue. (d) Bone scintigraphy shows increased tracer uptake at a site consistent with the left frontal bone lesion evident on MRI, and mildly increased uptake in the right parietal bone (arrow), but no pathological uptake outside the skull (e).
2188-4226-9-0383-g001.jpg
PMC9704848_01_2188-4226-9-0383-g001.jpg
g001
Acne was evident on the face, being especially severe over the outer left eyebrow area (Fig. 1a). Computed tomography (CT) revealed an osteolytic lesion on the left frontal bone (Fig. 1b). No increased uptake was apparent outside the skull (Fig. 1d, e).
Hematoxylin and eosin staining of the biopsied tissue. (a) Dense infiltration of neutrophils with mixed lymphocytes is evident. Large osteoclasts are also present. (b) In the center of the slide, a bone fragment with osteoblastic rimming and osteoid formation is evident, surrounded by fibrosis.
2188-4226-9-0383-g002.jpg
PMC9704848_01_2188-4226-9-0383-g002.jpg
g002
Histopathological examination revealed that most of the lesion was inflammatory granulation tissue, with dense infiltration of neutrophils (Fig. 2a). Bone fragments with osteoblastic rimming, osteoid formation, and fibrosis were also present in some areas (Fig. 2b).
Findings at the last outpatient visit. (a) Photograph of the acne taken 4 months after the reintroduction of isotretinoin. The acne has improved with scarring. (b) T1-weighted gadolinium-enhanced MRI shows the osteolytic lesion with slight contrast enhancement. Swelling of the surrounding tissue has improved.
2188-4226-9-0383-g003.jpg
PMC9704848_01_2188-4226-9-0383-g003.jpg
g003
The acne also showed improvement in comparison to the initial visit (Fig. 3a). MRI at the last follow-up point showed that the enhanced mass remained, but had shrunk (Fig. 3b).
Schematic chart of the clinical course and treatment of this case. The top row shows the our proposed diagnosis at that time. The middle row is a time series of the drugs used. The lower row depicts graphically the degree of pain in the left temporal region.
. 
Abbreviations: AMPC/CVA = amoxicillin/clavulanate; CNO = chronic non-bacterial osteomyelitis; LVFX/CLDM = levofloxacin/clindamycin; NSAIDs = nonsteroidal anti-inflammatory drugs
2188-4226-9-0383-g004.jpg
PMC9704848_01_2188-4226-9-0383-g004.jpg
g004
The above clinical course is presented in Fig. 4.