Light microscopy image of a lymph node biopsy stained with Congo Red and examined under polarized light. The tissue reveals extracellular, amorphous eosinophilic deposits distributed throughout nodal architecture consistent with amyloid. The deposits assume a dense, granular to plaque-like appearance on routine brightfield, and demonstrate distinctive apple-green birefringence when illuminated with polarized light, confirming the beta-pleated sheet rich configuration of amyloid fibrils. Congo Red positivity with birefringence distinguishes amyloid from other PAS-positive glycoprotein material and helps differentiate from non-amyloid nodal deposits. The beta-pleated sheet conformation accounts for the characteristic staining behavior and optical properties used in diagnosis. Clinically, identification of nodal amyloid supports systemic or localized amyloidosis and prompts workup for light-chain (AL) or serum amyloid A (AA) subtypes, including serum free light chains, immunofixation, and mass spectrometry-based typing. This image is relevant for educational illustrations of amyloid histology, pathophysiology, and diagnostic pathology workflows, including differential diagnosis with glycoprotein-rich PAS-positive deposits that are Congo Red negative. Potential clinical scenarios include workup of lymphadenopathy in patients with chronic inflammatory states, plasma cell dyscrasias, and lymphoproliferative disorders. High quality images like this support interdepartmental communication, teaching, and reproducible reporting of amyloid histology for junior pathologists and medical trainees in pathology education programs.

This renal cortical histology specimen demonstrates AL-type amyloidosis with kidney involvement in a patient with multiple myeloma. The left panel shows hematoxylin and eosin–stained tissue with amorphous, eosinophilic extracellular deposits within the glomerular mesangium and extending into the tubulointerstitium, causing mesangial expansion and variable basement membrane thickening. The right panel uses Congo Red staining to highlight the amyloid deposits, which appear salmon-pink on bright-field examination. Under polarized light, the same deposits display the diagnostic apple-green birefringence, a hallmark of Congo Red–positive amyloid. The deposits are diffuse, involving multiple glomeruli and extending into the tubulointerstitium, sometimes outlining capillary walls. In AL amyloidosis associated with plasma cell dyscrasia, the deposited light-chain–derived proteins disrupt normal renal architecture and contribute to proteinuria and progressive renal impairment. Differential considerations include AA (secondary) amyloidosis and other renal amyloidoses, but the combination of a known plasma cell disorder, Congo Red positivity, and apple-green birefringence strongly supports AL-type amyloidosis. This image serves as a valuable teaching reference for renal pathology, nephrology, and hematology-oncology, illustrating classic Congo Red histology, amyloid distribution patterns within glomeruli and interstitium, and the polarizing light signature. Correlates with proteinuria and renal dysfunction in many myeloma patients, guiding targeted therapy and monitoring of clonal plasma cell burden.

This histology image depicts human cardiac tissue (myocardium) stained with Congo Red and examined under bright-field microscopy. The image highlights extracellular, eosinophilic amyloid deposits that encircle and encroach upon individual cardiomyocytes (perimyocytic/interstitial deposition). The deposits appear as amorphous, orange to salmon-pink material on Congo Red, consistent with amyloid. When the same tissue is examined under polarized light, Congo Red–positive material exhibits characteristic apple-green birefringence, a pathognomonic feature of amyloidosis. The prevailing pattern is perimyocytic, with amyloid accumulating in the interstitium around myocytes and near small vessels, potentially contributing to myocardial stiffness and diastolic impairment. Histologic architecture shows preserved cellular morphology of myocytes with basophilic nuclei contrasted against the pink-red amyloid matrix. This image is diagnostic for cardiac amyloidosis on biopsy and would typically prompt typing (AL vs ATTR) by immunohistochemistry or mass spectrometry, as well as correlation with serum free light chains or transthyretin testing. Clinically, such infiltration predisposes to restrictive cardiomyopathy, diastolic dysfunction, arrhythmias, and heart failure symptoms. This slide underscores the utility of Congo Red staining in identifying myocardial amyloid deposits and the diagnostic value of polarized light birefringence for definitive confirmation. Useful for teaching, differential diagnosis, and research into infiltrative cardiomyopathies and treatment monitoring.

Imaging modality and technique: histopathology using light microscopy with Congo red staining of cardiac tissue, demonstrating characteristic amyloid deposition in the perimyocytic (pericellular) region of the myocardium. The deposited material appears orange to salmon pink on conventional hematoxylin-eosin–like chromogen, and exhibits classic apple-green birefringence under polarized light, confirming amyloid protein with a beta-pleated sheet configuration. The pattern is typically diffuse to pericellular around individual myocytes, producing a subtle, eosinophilic, amorphous coating that can obscure underlying cardiomyocyte detail. In this specimen, the amyloid is evident as an acellular, amorphous, hyaline-like material hugging muscle fibers, with irregular but cohesive contours and occasional nodular clusters. Congo red positivity combined with birefringence is diagnostic of systemic or cardiac amyloidosis when correlated with clinical data. Typing by immunohistochemistry, immunofluorescence, or mass spectrometry is often required to distinguish AL (light-chain) from ATTR (transthyretin) amyloidosis, which has implications for prognosis and treatment. Clinically, these deposits stiffen the myocardium, contributing to restrictive physiology and heart failure with preserved ejection fraction. The image illustrates foundational histopathologic criteria used in diagnosing cardiac amyloidosis and serves as educational material for pathology residents, cardiology fellows, and medical students studying protein misfolding diseases and Congo red histology. This image supports diagnostic confidence globally.

A three-part clinical photograph series demonstrating physical manifestations of systemic amyloidosis. Panel (a) presents an oral view showing macroglossia (enlarged tongue) with characteristic lateral scalloping, where tooth indentations are visible along the tongue's margins. Panel (b) shows the lower extremities of a patient in a supine position, highlighting a flexion contracture of the knee joint and associated muscle stiffness. Panel (c) displays a palmar view of the hand, illustrating sclerodactyly with thickened, stiffened skin on the palm and tapering of the fingers. These multi-system findings—encompassing macroglossia, joint contractures, and skin changes resembling scleroderma—are classic clinical signs of AL amyloidosis (light chain amyloidosis) and related plasma cell dyscrasias. The imagery serves as an educational resource for identifying the diverse musculoskeletal and soft tissue presentations of systemic amyloid deposition.

A composite of four clinical photographs demonstrating cutaneous and mucosal manifestations of systemic amyloidosis. Panels (a) and (b) show an intraoral and lateral view of the tongue, exhibiting significant macroglossia (enlargement). The tongue surface is irregular and bumpy, with prominent scalloping (crenation) along the lateral margins caused by indentations from the adjacent teeth. Panels (c) and (d) provide close-up views of the lower chest wall, displaying a dense distribution of small, discrete, waxy, papular lesions. These papules are flesh-colored to slightly erythematous and appear well-circumscribed. These findings represent classic diagnostic signs: macroglossia with dental indentations and characteristic papular amyloid skin deposits. The image is highly relevant for medical education concerning restrictive physiology disorders, plasma cell dyscrasias, and the physical examination of multisystemic protein deposition diseases.